Italian - In OTL Italian-Americans went to New York, Buffalo, Hartford, and Pittsburg, Italian-Canadians went to Toronto, and Italians in general went to Argentina; a majority of Argentines can be counted as Italian.
German - In OTL Germans populated Pennsylvania and later the upper Midwest; in the colonial era Pennsylvania was at one point half German-speaking and half English-speaking. In Canada they went to the Prairies, in particular Saskatchewan. The most German metro area in the US is Milwaukee.
Irish - In OTL the Irish settled everywhere, in particular around Boston and to a lesser extent Philadelphia. In Canada they went to the Maritimes, with PEI, Newfoundland, and New Brunswick counting themselves especially Irish.
Portuguese - In OTL the Portuguese congregated around Bristol County, RI and MA, and are found especially in Providence. In Canada they settled west of Toronto. Outside North America, they went to Brazil, of course, and to Venezuela.
Basque - OTL Basques mostly went to Spanish territories, as one might expect; a large percentage of Colombians, Argentinians, and Chileans are reckoned to be of Basque descent; they also figure into the early history of Newfoundland, and their flag is featured on the Saint Pierre and Miquelon flag. Recent Basques seem to have congregated in Idaho.
Indian - Indians tended to go wherever Britain colonized, as they were a plentiful source of cheap labor, for example in South Africa, Guyana, Trinidad, Mauritius, and Fiji. In modern times, the large number of educated Indians immigrating to North America have made them more plentiful. They congregate around Toronto, Vancouver, Calgary, San Jose, and Trenton. In TTL, their location will depend heavily on their actual history; if India has a history with more European powers, they won't have that kind of geographic preference.
Lebanese - As the only large Christian Arab population, Lebanese have represented the majority of Arab immigrants in western countries until recently. In the New World, they tended to settle in Brazil, Argentina, and Australia, with a significant number settling in the Dominican Republic. In the US, they congregated in Detroit, Boston, and Paterson, New Jersey. In Canada, Lebanon's connection to France led most Lebanese to settle in Montreal and Ottawa.
Polish - Polish in the US are associated most strongly with Chicago, but there are also large concentrations in Milwaukee, Buffalo, and Presque Isle, Michigan. In Canada, they settled in Toronto and some of the Prairie states, particularly Manitoba. A significant number went to Brazil, where they concentrated in Curitiba.
Chinese - Somewhat predictably, the Chinese have had their strongest influence on the West Coast, especially San Francisco, with the largest number on the East Coast going to New York. In Canada, they are especially populous in Vancouver, Toronto, and Calgary. In Latin America, Chinese did not settle heavily, although a respectable number settled in Venezuela.
Scottish - In the US, the states with the highest proportion of Scottish ancestry are Maine, Utah, and New Hampshire. In Canada, literally every province reports higher numbers of Scottish ancestry except for Quebec, Nunavut, and Newfoundland-Labrador; the highest proportions are in PEI and, of course, Nova Scotia. A respectable number of Scottish settled in the far south of Chile and Argentina.
Filipino - The large number of Filipinos in the US can be attributed to the colonization from 1900-1946. In this time, the country switched from Spanish to English. As expected, Filipinos settled mainly in Hawaii and California; unexpectedly, they form the majority in some small Alaskan fishing villages, though they probably are not permanent residents there. In Canada, Filipinos went to Toronto, Vancouver, and Winnipeg. In TTL, we would probably expect them to instead go to the Spanish-speaking ASB states.
Pakistani - Most Pakistani follow Indian patterns of settlement, owing to their shared heritage as a British colony; their New world population outside the anglosphere is negligible. In the US, they mainly congregate in the NYC metro and other large cities. In Canada, the outright majority of them live near Toronto.
Albanian - Most Albanians in the New World arrived as a result of the Kosovo crisis in the 1990s. Many live in the New York metro, but an older community resides in Detroit. In Canada, most Albanians reside in Toronto.
Jewish - The United States has historically been one of the few countries to accept Jewish immigration. American Jews are concentrated in New York, and a large number of them are moving to Miami and Los Angeles. In Canada, Jews congregate in both Toronto and Montreal, the latter owing in part to the robust Jewish population in France.
Armenian - Armenian immigration has been driven by continued instability in the Caucasus region and oppression by the Ottomans, Soviets, and Iranians; in the United States, most Armenians settled in the Los Angeles area, particularly Burbank. In Canada, Armenians congregate in both Montreal and Toronto, though more heavily in the former. In Latin America, Armenians concentrated in Montevideo and Buenos Aires.
Arab - Historically, most Arabs traveling to the New World were Lebanese; in more recent times, Arabs from other countries have immigrated as well. In the US, Detroit has been the center of Arab immigration, while in Canada, the connection between France and Lebanon has led to Montreal being the major center.
Norwegian - In the US, Norwegians took to farming, and settled heavily in North Dakota, Minnesota, and South Dakota. Similarly, in Canada, Norwegians settled in the Prairies, particularly Saskatchewan.
Swedish - Similarly to the Norwegians, Swedes settled in the northern plains states, although the Swedes settled most heavily in Minnesota. In Canada, they went to places like Winnipeg, Calgary, Edmonton, and Vancouver. In Latin America, they went to Misiones province in Argentina, which is adjacent to Paraguay and Brazil.
Bengali - Due to its colonization by the British, Bengalis in the Western hemisphere are almost exclusively settled in Anglophone countries. They tend to follow other South Asian settlement patterns, being heavily settled in New York city, Toronto, and Vancouver.
Greek - Greeks in the US are concentrated in New York, Boston, and Chicago, although Pinellas Springs in the Tampa area is most strongly Greek in heritage. In Canada, the largest Greek community is in Toronto, but the area with highest concentration is in Laval, Montreal CMA. In Latin America, Greeks were attracted to Saltpeter mining in Antofagasta, Chile, although most of them moved south to Santiago and Valparaiso.
Nigerian - Nigerians in the United States are clustered in New York, Dallas, Houston, and the DC area, while Nigerians in Canada are concentrated in Toronto and Brampton.
Russian - Political developments in the USSR strongly influenced patterns of Russian immigration in the US, from the white emigres to the post-Soviet economic collapse. Russian-Americans are concentrated in the New York area, although some villages in Alaska still use the language. Russians settled in few other New World countries; in Canada they concentrated in Toronto, Montreal, and Vancouver, while in Mexico there was a short-lived Russian utopian community in Ensenada.
Vietnamese - Refugees from the Vietnam War are the biggest component of the Vietnamese-American population. In the US, they settled in Los Angeles, San Jose, and Houston. Despite the connection between France and Vietnam, Vietnamese mostly settled in Toronto rather than Montreal.
Moroccan - Due to France's connection with Morocco, the vast majority of Moroccans settled in Vancouver. In the United States, they are centered in New York City, with some concentration in Jacksonville and Boston.
Ukrainian - Ukrainians were more attracted to Canada than to the US, particularly Saskatchewan; Winnipeg, Edmonton, and Saskatoon all have large numbers of Ukrainian Canadians. In the US, the largest group is in New York, but the highest concentrations are in Philadelphia, Seattle, Portland, Pittsburgh, and Cleveland.
Japanese - Japanese were not really attracted to the United States, except of course Hawaii, where they are one of the most populous ethnic groups, and in Los Angeles. Instead, they went to Sao Paulo and Lima.
Igbo - After the Biafra War ended in 1970, many Igbo emigrated to Canada and the US. A large number of imported slaves were Igbo, but this older group has been subsumed into the wider African descended communities. Igbo tend to follow the pattern of other Nigerians, settling in Houston, the DC area, Toronto, and Vancouver.
Korean - After the Korean War, many Koreans emigrated to the US for opportunities. They settled especially heavily in Los Angeles and New York; the municipality of Palisades Park, NJ, is IIRC the only Korean-majority municipality outside Asia. In Canada, Koreans are concentrated in Toronto and Vancouver. In Latin America, many Koreans transited into Paraguay and then transited illegally into Brazil and Argentina, which had established Korean communities associated with their Japanese communities.
Berber - There are very few people in the US who identify as Berber; most North Africans instead list themselves either as Arabs or according to their nationality. In Canada, they are most heavily concentrated in Montreal.
Sri Lankan - Like the other South Asian ethnic groups, Sri Lankans mostly went to Anglophone countries, particularly Canada; most Sri Lankan Canadians live in Toronto.
Syrian - Christian Syrians tended to follow their Lebanese counterparts to Brazil, Argentina, and Quebec; in more recent times, Canada's greater acceptance of Syrian refugees in the wake of the ongoing civil war has led to the Syrian population growing substantially. Also of note are Syrian Druze, who make up the majority of Venezuela's Middle-Eastern population.
Indonesian - The United States has not traditionally been a significant destination for Indonesians, as it was historically easier to settle in the Netherlands. In the US, many Indonesians live in Southern California, although many Indonesian-born Americans were actually of Chinese descent, having been expelled after independence.
Welsh - In the United States, self-identified Welsh people are concentrated in Salt Lake City, Philadelphia, and Columbus. Historically, they made up a large part of Pennsylvania and Ohio. In Canada, the Welsh settled most heavily in Alberta. In Latin America, of course, many Welsh traveled to Patagonia, where a Welsh community still thrives.
Kurdish - The largest Kurdish population in the US is in Nashville; many Kurds came to the US as refugees who fled Iraq after supporting the 1991 Gulf War. Today, more Kurds settle in Canada, both in Toronto and in Montreal. Kurds have not historically had a united diaspora movement, owing to the differences in both language and nationality among Kurds.
Sikh/Punjabi - There is a significant difference between Sikhs and Punjabis, but most of the Punjabi immigrants to the US and Canada have been Sikh, so I have included them here. Punjabis are most concentrated in Vancouver, due to Canada's connection with the British Empire. In the US, most Sikhs settled in California.
Romani - Many Romani traveled to the New World to escape persecution in Europe. Very few of these settled in Canada; in the US, they settled in many places; the exact distribution is not tracked by the census. Antiziganism never really took hold in the US for some reason; until recently, many Americans believed "Gypsies" to be a myth. Most Roma in the US are descended from those who lived in the former Austro-Hungary. In Latin America, the Spanish and Portuguese Roma traveled to Argentina and Brazil.
Bihari - The first wave of Indian emigrants, mostly indentured laborers sent out to sugarcane plantations in other British territories, were overwhelmingly Bihari. In Mauritius, Trinidad, and Guyana, these were mostly Bihari, while in Fiji there were Awadhis (which neighbors Bihar) as well.
Thai - The vast majority of Thai in the US settled on the west coast, and comparatively few of them chose to settle in Canada. The anglophone country with the highest proportion of Thais is New Zealand, at 1.2%. On the US east coast, Thais are concentrated in Tampa and New York.
Iranian - Many Iranians fled to the US and Canada after the Iranian Revolution in 1980. These concentrated overwhelmingly in the Los Angeles area, which has 1/4 of the US total. In Canada, they tended to settle in Toronto and Vancouver. The east coast centers of Iranian settlement are in New York, DC, and Baltimore.
Romanian - Due to a 19th century push by Canadian Minister of Home Affairs Clifford Sifton, Romanians from Bukovina, Austro-Hungary, tended to settle in Canada more often than the US. They tended to congregate in Ontario and Montreal, but several settlements in Alberta were founded by Romanians. In the US, they concentrate nowhere in particular. Brazil also attracted Romanians.
Hungarian - Cleveland was the single largest concentration of Hungarians in the western hemisphere in the mid-20th century; the first came from Austro-Hungary in search of opportunity, while the last major wave came from Communist Hungary following the failed 1956 protests. Other major destinations were Pittsburgh, New York, and Chicago. In Canada, there are Hungarian settlements in the prairies and enclaves in the cities. Many of Hungarians worked on the Welland Canal near Niagara, while others settled in Prince Edward Island.
Danish - Many Danes in Europe joined the LDS church and moved to Utah in the mid-19th century. The largest concentrations of Danes in the US outside Utah are in Omaha and Minneapolis. In Canada, Danes tended to settle in New Brunswick.
Tamil - Sri Lankan Tamils tended to move to Canada, while Indian Tamils tended to move to the US. Canadian Tamils concentrate in eastern Toronto, while American Tamils tend to live with the other Indian ethnic groups in New Jersey. Many Tamils were taken from French India to the French Caribbean and Guiana as indentured servants.
Swiss - The Swiss were more attracted to Argentina and Chile, where they went to Santa Fe province in the former and Punta Arenas, Valparaiso, and Temuco in the latter. In Brazil, Swiss settled in the southeast around Rio de Janeiro State, while in the US, most swiss immigrants were Swiss Amish, who are concentrated in rural Indiana and to a lesser extent Wisconsin.
Croatian - Croatians were very attracted to Chile due to the Tierra del Fuego gold rush; they form an important part of that region's population. In the US, they were attracted to Pittsburgh, Chicago, and Youngstown. In Argentina, they settled in rural Buenos Aires Province, while in Canada, they settled the prairies, particularly Saskatchewan.
Serbian - Many Serbs emigrated long before the breakup of Yugoslavia, and likewise many of them identify as Yugoslavians or do not distinguish between themselves and other Serbo-Croatians. As a result, it is difficult to say for sure where Serbs settled. Certainly, there was a population in Alaska that came during the Yukon gold rush, and certainly, some emigrated to Argentina, but exact figures are hard to come by.
Iraqi - Due to the US-led invasion in 2003, many Iraqis fled to the United States; however, the US's inconsistency towards muslim immigration and asylum seekers have led many Iraqis to settle in Canada instead. Iraqis tend to identify themselves as Arabs, Kurds, or Turkmen rather than Iraqis, so in the US they tend to settle where other Arabs settle, especially the Detroit area.
Czechs - East-Central Texas attracted a large number of Czechs, especially Moravians, many of whom fled Austro-Hungary after the Revolution of 1848. Other Czechs settled in Iowa and Nebraska, where they have high concentrations in Omaha, Cedar Rapids, and Lincoln; these were largely Bohemians, but in most cases the distinction between the two has not been very sharp.
Ghanaians - As one of the most stable and successful nations in post-British Africa, Ghana has provided a great number of immigrants to the Anglosphere. In Canada, many Ghanaians settled in Toronto, while in the US, many Ghanaians settled in the Bronx, the DC area, and the Columbus area.
Lithuanians - The US attracted the most Lithuanians, followed closely by Brazil and somewhat distantly by Canada. In the US, the Chicago area is more strongly associated with Lithuanians, while in Brazil, the state of Rio Grande do Sul and Sao Paulo attracted the most. In Canada, the outright majority live in Toronto.
Assyrians - Also known as Chaldeans or Syriacs, this group is one of the smaller ones in the new world. They first came as refugees from the Assyrian Genocide in the Ottoman Empire, while others came from Iraq as refugees from Saddam Hussein's regime. Assyrians in the US settled in Detroit alongside existing middle-eastern communities, with smaller groups in San Diego and San Jose; in Canada they are concentrated in Toronto.
remainder under construction
Azerbaijani - People from what is now Azerbaijan came to the US following World War II. However, most of them came to the US from Iranian Azerbaijan; these settled on the west coast with other Persian groups. In Canada, most live in Toronto.
Cambodian - Despite Cambodia's background as a French colony, the proportion of Cambodians in France and Canada is not significantly higher than in the US. In the US, there are significant populations in the Los Angeles area, particularly Long Beach, and also Boston (Lowell) and Tacoma.
Somali - Most Somalis came to the US as a result of the civil war beginning in the 1990s, and they settled in Minneapolis and to a lesser extent in Columbus. In Canada, they settled in Toronto and Ottawa.
Afghans - Immigration stepped up after the invasions in 1979 and 2001; due to Canada's more lax refugee policy, Toronto is probably the biggest concentration of Afghans in the western hemisphere, followed by the Bay Area. Afghanistan is home to a variety of ethnic groups; prior to 2001, 2/3 of the US afghans were Tajik; now, there is more of a mix.
Mennonites - While primarily a religious group, the endogamy and isolationism that some Mennonite communities practice makes them arguably a full-fledged ethnic group. Most of these groups in the New World live in Pennsylvania, Ohio, and Indiana.
Malay - Most Malays outside Asia traveled to South Africa instead of North America; many also settled in Australia. In the US, Malays settled in New York and Chicago, and in Canada, they mostly settled near Toronto.
Bulgarian - Bulgarians in the United States have been immigrating for a long time, in relatively small numbers, and are very diffuse. The major concentrations, if they can be called as such, are in New York, Chicago, Los Angeles, and Las Vegas. In Canada, most Bulgarians were historically from what is now North Macedonia, and they settled in and around Toronto.
Catalan - Catalonia has been part of Spain for so long that its emigrants have generally assimilated quickly. The country with the highest proportion of Catalan ancestry is probably Argentina, but hard facts are difficult to come by since Catalans were simply recorded as Spanish. Cuba probably also has a decent number.
Macedonian - Many Macedonians traveled to Argentina and Brazil as seasonal workers, although quite a few of these were actually Aromanians and Megleno-Romanians, who had a common Latin background. In Canada, Macedonians settled in the Toronto area, while in the US, Macedonians settled in New York and Detroit.
Yugoslav - In the United States, many people from former Yugoslavia still identify as Yugoslav. Most of these emigrated during the cold war, when Yugoslavia was united, and are probably Serbian in background.
Turkish - Turks are a very widespread ethnic group in the old world, owing to the successes of the Ottoman Empire. Many Turkish emigrants were Cypriot in origin, as Cyprus was ceded to the UK in 1878. Many Turks historically emigrated to Australia, particularly Melbourne and Sydney. In the US, most Turks settled in greater New York, particularly the New Jersey side, and also places like Houston and Jacksonville. In Canada, they settled in Toronto.
Jaffnese - A term referring to Tamils in Sri Lanka, the Jaffnese emigrated en masse after Black July in 1983 and the ensuing Civil War. They traveled overwhelmingly to Canada rather than the US. The greatest concentration is in Toronto, but Montreal, Ottawa, and Calgary all have populations as well.
Bosnian/Bosniak - Technically, a Bosniak is a muslim Bosnian, but it is difficult to find figures differentiating the two. Most came to the New World due to the 1990s Bosnian War. In the United States, St. Louis is the center of the Bosniak diaspora, followed by Chicago, while in Canada, that is Toronto.
Hmong - The US recruited Laotian Hmong heavily to fight against the Viet Cong, so a large number of them were evacuated in the Fall of Saigon. Many of them settled in Minneapolis, Fresno, Sacramento, and Milwaukee.
Maltese - Melbourne's western suburbs are the largest concentration of Maltese outside Afro-Eurasia. In Canada, they went mostly to Toronto, while in the US, they concentrated in Detroit. Some Maltese in the US were classified as Italian. Some of them went to Puerto Rico.
Lao - Following the Communist takeover of Laos, many Laotians traveled to France, the US, and Canada. In the US, they settled in west coast cities like Sacramento, Fresno, Nashville, and San Francisco. In Canada, most live in Montreal, Vancouver, and Toronto.
Ethiopian - Ethiopia is comprised of many ethnicities; the largest overseas are the Amhara while the largest in-country are the Oromo, and others include Tigrinya. Ethiopians in the US are especially prevalent in the Washington, DC area, while in Canada they congregate around Ottawa.
Congolese - Following the Second Congo War of the early 2000s, many Congolese left Africa as refugees. In the US, there are significant populations in the DC-Baltimore area, as well as Boston, New York, Dallas, and North Carolina. In Canada, they congregate in Quebec.
Zimbabwean - Referring specifically to black Zimbabweans, whites being considered Rhodesians. Zimbabweans fled their country during Mugabe's long and authoritarian rule; few settled in Canada, but many settled in places like California, New York, and Texas.
Latvians - Historically, Latvians were among the people who settled the Canadian prairies in block settlements. In the US, Latvians are one of the smaller Eastern European ethnic groups, many living with other Eastern Europeans in New York, Chicago, and Philadelphia.
Samoan - Since the annexation of East Samoa to the US, many Samoans have moved to the mainland. Los Angeles and San Diego have the most, while a surprising number have settled in Alaska.
Cabo Verdean - The archipelago was first inhabited by Portuguese, who quickly brought African slaves to work there. Most Cabo Verdeans live with Portuguese communities in southern Massachusetts.
Galician - It is difficult to differentiate Galicians from other Spanish ethnic groups in historical records, but it is believed that most new world Galicians live in Argentina and Uruguay, with a significant portion living in Cuba.
Icelandic - Most Icelandic people in the New World, as previously mentioned, moved to Canada, especially the Lake Winnipeg region. The first Icelandic immigrants were largely Mormons.
Hawaiian - Since the annexation of Hawaii in 1899, many Native Hawaiians have moved to the mainland, mostly to California.
Pashto - The dominant ethnic group in Afghanistan, many fled for the US after 2001. The largest centers of Pashtun population in the US are New York, San Francisco, and northern Virginia.
Eritrean
Volga German
Sudanese
Yemeni
Kashubian
Montenegrin
Estonian
Sindhi
Tibetan
Zoroastrian
Moldovan
Circassian
Moluccan
Uyghur
Oromo
Cham
Chechen
Frisian