I don't think it's the primary reason.

The Canadian tech sector doesn't make nearly as much money as their US counterpart does. The country has very few dedicated software companies, and none the caliber of the FAAMGs. For comparison, the largest software company in Canada by revenue earns $1.7B, Google is in the neighborhood of $120B a year.

Google/Microsoft/Facebook/Apple/etc are each individually orders of magnitude larger than the entire Canadian software industry combined. Chances are, that most metro areas in the US have a technology company larger than the biggest Canadian tech companies.

If Canada went from having a billion dollar tech sector to having a trillion dollar one, then salaries for engineers would explode.