As someone who graduated from Computer Science at Waterloo, this is common for anyone with the ability to do so. Pay is not competitive in Canada, and contrary to the common refrain here, taxes/rent/general CoL does NOT make up for this, not even close.
It's not just the taxes/rent/COL. I know three Canadian SWEs whose parents could have easily bought them a nice house or condo in any major Canadian city, if they had wanted to stay. One of them explained it to me this way: the quality of employers, coworkers, and the overall software engineering work you'll do in Canada just doesn't compare to the US. Even if pay/finances were exactly the same, going to the US would…
From my experience, the only place the last statement hasn't been true is Montreal.
There are a lot of engineers over there that could move but won't ever. That's partly why everyone is setting AI shops over there.