The size of the pay difference is something you, as the prospective employer, have significant direct control of. It is within your authority to point the dial anywhere from "hard to find anybody because of the massive pay difference" to "easy to attract strong talent, while still saving money relative to what it would cost to attract the same level of talent in the US".
The Canadian business establishment will not come after you to break your knees if you offer higher wages than they do.
(Later a large part of our staff was Canadians returning home in 2016 after doing their time in Mountain View)
I've worked for many companies over the years that chose to colocate here because of the relative ease of finding talent.
And there's plenty of good talent that doesn't leave. Because we don't want to. Home is home.
There's also lots of us who work remote for US or EU companies these days.
(Blackberry movie also is garbage)
It's easy to knock Canada for its personal income tax rate, but compared to European alternatives, it's still quite low, despite offering a whole lot of baseline public goods.
That said, while senior SWE salaries here absolutely not even close to competitive with the Bay Area or NYC they are not that far off from other places in the US (like smaller midwest cities etc). While Canadian salary packages are depressed, it's also partially a result of: they're not inflated.
The bigger concern is more the lack of interesting work.
Many do similar calculations. Home is home. It's profoundly arrogant (and very American) to assume that the "best talent" moves for money and opportunity.
Americans have very high labour mobility rates, and often assume that's how the whole world works. But in most places in the world the idea of uprooting your whole life for a job is seen as odd.