You're right about the comparison between Seattle and Vancouver, but "housing is half the price" is a common comment from Canadians that have made the move (both online and people I know personally). It may be an exaggeration, but the US has 10x the population and more medium-large cities to choose from so I think it's somehow true at least some people can find a significantly cheaper place that is personally comparable and has a job for them. If you're a software engineer that lives in Vancouver (1x salary, 1x housing prices) and loves the mountains and wants to move to another mountain-adjacent place, Denver (2x salary, 0.5x housing prices) is indeed pretty enticing compared to Seattle (2.5x salary, 1x housing prices) or Calgary (1x salary, 0.4x housing prices).[1]
I agree. There are lots of places in Canada with 0.3x house prices but once you filter for 1x salary and places which are nice to live in Canada you are left with an empty set.
The ideal situation is you get a remote job in Canada for 1x salary and live in a nice place with 0.3x houses. That is my current setup.
[1] Guess but not complete wild-guess multipliers