I used to assume a border which would probably be wrong; but I'd revise it thus
- It would include Labrador, but the Abitibi and Nouveau-Quebec/Nunavik areas would not be part of it.
- It would probably include part of, but not all its ontario claims, following the same line as its OTL southern border: roughly, this means Ottawa and Sudbury in, Toronto and Windsor out. Basically, Eastern Ontario at its smallest extent, Northeastern Ontario, but not the districts of Cochrane, Timiskaming
- The peninsula would receive the same treatment as the other contested areas; I learned last week that NY actually claimed it.
- Finally, Maine would get the border counties of Quebec, the area known today as Beauce, more or less.
Assuming a rough division of today's divisions of the area
- A state of Quebec (I suspect it would be renamed Canada) - Area would be about 960,000-1,000,000ish square km, depending on the exact division of Ontario and the west and where Maine's final border are. Thunder Bay would probably be contested: kudos if you manage to turn it into a state (bonus points for an Ojibwe majority), but I don't think it could handle the density
- population would be about 9-9.5 million. It may end up being treated like Mass+Maine or North Carolina and Tennessee, even though this part of the area has no conflicting claims as far as I could tell, and population wise, this particular region wouldn't hit the 80,000 rule of thumb before the 1840s, maybe even the 1860s.
- A state of Ontario, Erie or Huron depending on which lake gets picked. Population would be 10.5-11 million, area would be a bit less than New York but not significantly so. These areas are also largely devoid of French Ontarians IOTL.
- The rest of the north would be huge, but would also have fairly low immigration; I suspect it would be added to Manitoba for some (probably named Assiniboia), and turned into its own "Western Alaska" for the rest. Probably called Timiskaming, population about half a million. It would be over a million square km.
- Whatever happens to the prairies, well, I had a map, but I admit that I based it off Canadian terriroty borders from the 1800s, which IIRC were not quite set at that point. The area which is included in the northern prairies is about half a million km2 (including Thunder Bay) and has a population of a quarter million people today.
Manitoulin would probably be contested between everyone who has access to Lake Huron. I'm not sure if it was in the NY claim area; if yes, it goes to Ontario, if no, it has strong chances of going to Quebec or whatever gets formed from the lands north of the NY Ontario claim zone.
I could also see the units being cut smaller, but the problem with cutting Quebec down is the same problem there would be with cutting Alaska down and the same problem you had with the Jefferson map of the Midwest: yes, geographically they would be equal in size, but agriculturally/supporting capacity wise, they would be condemned to remain minor states - it's not impossible to live with it, obviously, New England manages, but yeah. One reason I could see Quebec split in two would be a Tennessee situation, but yeah. Of the 9.5 million I posited, only about 1.5-2 would be on the "Ontario" side.