Unlike Canada, California benefits from a pool of ~290 million other people who self-select to move there with 0 barriers other than having a few dollars to buy a gray hound ticket.

Is the cost of housing a barrier?

If you're asking this seriously... yes it is a barrier, but not as great as Immigration/moving to a completely new country.

Which is not to discount California's tremendous housing crunch. I am merely pointing out that its a much lower risk for a young single US citizen to just move to CA, try it out for a few months, if they can't get a job or make it, then just drive back. It is much harder for people from outside the country to do the same.

Not really. The cost of housing is huge and a barrier if you are not in tech, But if you move for tech you can definitely find a place and pay the crazy rent with your new salary.

That's very true.

As per the comment below, the population between Vancouver, Toronto and Montreal is about a third of the total population (about 12M).

Bit pedantic but this really is a far cry from being the "vast majority" of Canada's population.

Golden Horseshoe is 9.2 million alone. So 12 million is definitely on the low side.

Yeah, I guess (I was curious, and you're right, about 1/3 live in Vancouver, Toronto, and Montréal metro areas), but (to me) the culture varies a lot more between Toronto and Montréal than between SF and, I don't know, some of the more rural parts of California. Thinking like a business, the difference in regulations is much more significant as well.