So, here's my alternate history Canada/US boundary - extending due west from the western tip of Lake Superior until the Snake River, then following the Snake until the Columbia River and then on to the Pacific Coast (follow the red line).
Canada would have been given the top third of Minnesota, about 3/4 of North Dakota, half of Montana, the northern sliver of Idaho and almost all of Washington state.
Frankly, except for Washington state, the US wouldn't even notice the loss of this strip of land, but look at what a tremendous difference it would make to western Canada. In the Prairies, it would increase the amount of farmland and rangeland available by well over 50%. There would be room for 2-3 more major prairie cities. The Pacific coast of Canada would receive a huge boost. I imagine there would be a major megalopolis extending from Vancouver south to Puget Sound.
Instead of 12M people living in western Canada, I imagine the population would be over 20M. This would be close to the 25M living in eastern Canada and would certainly change the power dynamic of confederation.........