Gotta pay more money to keep the talent. This isn't rocket science. The crazy thing is Canada has so many advantages that should make paying higher salaries easier. University is cheaper, so people don't have as much (or any) student debt. Healthcare is cheaper for companies to provide - since they generally only have to offer supplemental coverage. And so on.
But aren’t those things cheaper because there are more taxes? And more taxes mean less salary?
1) You will likely pay more in taxes in California than Canada.
2) It's easier to itemize self-employment tax expenses in Canada, so you can easily pay half the taxes of the US. (I paid 12% of total income the last year I worked in Toronto.)
3) Everybody I know in Canada is happy with health care, and infinitely happier than Americans who've received false bills.
4) Startups have a big advantage in Canada because of the state health care, and unrelated lower salary expectations.
However, salaries are lower in Canada because companies pay less (like Europe or anywhere outside the US), but that's not related to taxes or health care.