That's a lot of hypotheses: Americans migrating to Canada may be in specific professions (though the same is true for Canadians emigrating to America), or they may all be Americans who have married Canadians (though this would beg the question of why Canadians who marry Americans don't move south), or they may all be skilled immigrants who are giving up on Canada (though if this were true, then they would still count as Canadians emigrating to America, and be fewer than Americans emigrating north).
As for your Canadian friends encountering headwinds when they move back to Canada -- that's normal, when you relocate in middle age. Why are they moving back to Canada? Because the financial sector in the U.S. went through a near-collapse and reorganization in 2008-2010, and they lost their jobs. Why Canada? Because Canada's didn't -- and now they're starting out again, and competing with locals and all the other people coming home. And that question about Canadian experience? That's because there are Canada-specific aspects to finance -- just because one has worked on Wall Street or in Tokyo doesn't mean that they are superbly qualified for Toronto. And because these aren't huge barriers, they probably found work, eventually.
It's interesting that native Canadians are asked that as well, it suggests that the motivation is simple (a desire for Canadian experience) and not racist.
The fact remains, for the past few years more people have come north than have gone south.