Uh.. I have to disagree here. Manitoba isn't really a possibility until after the 1800s. Ontario and Nova Scotia would be a lot bigger earlier on with more Loyalist settlement, and it would lead to an earlier expansion into Manitoba but not expansion to there right away. The reason is hereww12.statcan.ca/census-recensement/2006/as-sa/97-550/vignettes/img/map-2006-pop-density-canada-sz01-en.gif"]reason is here[/URL]. As you can see, most of Western Ontario is pretty sparsely settled with a large gaps between Manitoba and Ontario. Those gaps aren't just pure luck; that areas horrible to build on and hard to travel through.
I highly, highly doubt this. Even if you assume that all 70,000ish end up in Canada (46,000 did IOTL), the probability they'd settle in Quebec (of which the only real part available for settlement was the Eastern Township, now entirely Francophone despite it not being the case at all 100 years ago) over the free land tracts in New Brunswick, Nova Scotia and Ontario is... not very likely. Quebec still had its own civil code recognized by the British and was run by the Catholic Church. The seigneuries were kept and most of the land along the St. Lawrence was already owned by someone. Many of these UEL will not want to live in an occupied territory like that. What's more likely is you'll see an earlier boom in Ontario and Nova Scotia's population and faster growth in Ontario, with more Loyalist sentiment perhaps creating more conflict long-term with Quebec. Don't think it would affect the border more than anything else; Canada could've had a more southern border but the Brits chose against it. -shrug-