Dutchie
Its definitely a far more likely way of the US taking over western Canada than what Eurofed's suggesting. There was a lot of concern about the American settlements of their adjacent area leading the the region being drawn into the US political sphere OTL. Avoid the 1812 conflict and you would continue to have substantial US settlement in Canada, which might have either led to a stronger Canada or it being steadily absorbed into the US.
One small quibble. Unless I'm badly off it was the HBC [Hudsons Bay Company] that control the bulk of the area under discussion. They did discourage settlement to avoid disruption of their fur interests and this went on so long that it made the area very vulnerable to American encroachment. Could have had something making this lasting longer and with better Anglo-American relations might get the results your talking about.
Steve