Paul Spring said:
By the 1820s Ohio, Indiana, and Illinois were settled enough to be states, and Michigan followed within a few years. They weren't densely settled, but they were more densely settled than most parts of Canada. No matter how you look at it, at least half of the settler population of everything south of the Great Lakes is going to come from the US - and that's a very conservative estimate.
The same thing is probably going to be true later on for the northern plains states, and also the Oregon territory. OTL the British gave up control of the southern part of the Oregon territory because the vast majority of the people settling there were from the US. In an ATL with a weaker US, Britain will probably control the whole territory, as they would the area around the Great Lakes and the prairie provinces, but they will have to face the fact that a large portion of the population (50% or greater) will not come from Britain or British territories, and won't think of themselves as "British". That's hardly an insurmountable obstacle - in OTL a large portion of the settlers in the Canadian prairie provinces especially came from the US, and they ended up just as Canadian as the other provinces.
Michigan in 1810 had a population less than 5000 by 1830 it was only 28,000
settlement in the northwest in this period largely confined to the states of the Ohio River and in the Trans-mississippi ( Missouri, Louisiana and Arkansas, all three out drew settlers from the northern tier of the northwest.) largescale settlement in Michigan does not occur until the '30's, Wisconsin...'40's. Arguably the preference for settlement will be in the lands further west which are more easily accessible. These will be along the lines that are most easily accessible and that will be the Ohio and Mississippi Rivers. Arguably Michigan and Wisconsin are far more accessible from UC than they are from the rest of the US, at least until the opening of the Erie Canal anyways.
In a TL where Britain obtains control of Michigan and a protectorate over the Indian lands of say Wisconsin this will be even more so, but the effect is still not going to be felt to any great extent until the 30's. Arguably those people that Came to BNA and then moved on to the US instead in O"TL will no doubt simply settle in first Michigan and then in Wisconsin as the Br. authorities obtain clear title from the natives. They will not allow settlement until that is done given that the Natives have been their allies in this War of 1812.
As to settlement on the prairies except for the Red river settlement , there was not largescale settlement until the '90's largely because of its physical separation from the settled areas by the expanse of the Cdn shield. This will not be the case here. Settlement will progress westward through Michigan from UC to Wisconsin and then into the Upper Red river. probably as fast as it did in OTL but almost assuredly from Br/BNA or European sources. As I stated earlier a great many people initially migrated to BNA and simply moved on to the US because of the greener pastures there. That will not be the case. Far more of them will remain in BNA, as many of those that went to the US will arguably simply move to a Br. Michigan and Wisconsin instead. this could even lead to a more northerly BNA version of the Oregon trail. say accros s the Upper missouri, though I am not sure where they would cross the Rockies. There are no easy passes there. This will make for a larger pool of BNA settlers to draw on in the push to settle the prairies than in OTL. Greater Br sponsored settlement ( non-american ) in Michigan and Wisconsin will fuel greater Urban growth and Industrialisation in the U and LC because they will provide a larger market for their goods as well as those of Britain.
The Selkirk settlement will likely be larger in this TL ( encompassing the entire Red and Assiniboine River basins and might even be in Michigan instead of Manitoba. The initial Settlers there were recruited from Scotland, not the US. If the grant is larger there will be a larger Scottish/British presence and eventually Metis presence. If the British are given clear title to the entire Red River, as was posted by someone else in conjunction with pressing to the fullest their claims in Oregon, then argueably the the border parallel in the west across the prairies will be drawn further south than OTL. Those lands are after all unsettled for the most part in the aftermath of 1812 and there is no point quibbling over virtually empty space. If more land is available for settlement...more French Cdns will be drawn west than to the N.Eng mill towns. Others could be drawn to a faster growing Montreal fueled by the larger market to the west.
I am sorry but I have to reject in its entirety your suppositions that the British would be overwhelmed by Americans moving west. It did not occur in OTL largely because there was substantial land available for the taking in the trans-Mississippi and then the Far west.. This will be the still the same in this TL. There will be an initial aversion to moving to Br. terr. in the aftermath of this war and there will be no need to be seeking terr. to settle in the north.
they will simply push west and Sw a little earlier in this TL. Earlier confrontation in Texas perhaps and even California. of Course this really depends on the outlook of the Br. in this TL, though it should not be radically altered as long as the American and Br. gov'ts continue to follow the pragmatic compromise course that they did OTL. There is no reason to assume they will not either.. Unless NEng succeeded or something..which changes the picture dramatically, that is only going to occur if the war were to have gone overly long, something that the Americans could not have sustained simply for financial reasons. Its possible though I suppose but the suggestion that a more favourable adjustment in Northern Maine is obtained seems a bit more likely. the N. Englanders would have to be pretty annoyed with Washington to succeed, and they would have to do it while the War was in progress to get away with it unless New York goes with them.