Nationalism and Protectionism. In the case of Canada, left-wing Nationalism affects a lot of Canadian-US relation policy and trade. In short Canadians really hate Americans and do not wnat their industries overtaken by US. They're really insecure about their national identity
Skilled Work Visas are a more compleicated issue than we might realize. Not because of larbor staturation (it's skilled labor so it's meeting a deficit), the problem is a concept known as brain drain. You get this with software companies sniping other developers (hiring them for higher wages). Essentially all the smart and well educated people in your country leave and go to somewhere else that pays more. As a result the country that educated you and raised you gets nothing and you get paid higher wages which no tax benefit goes back to your country of origin. Poor countries get poorer and rich countries get richer and mroe talent. It's a on going problem with globalism and most economists are aware but don't have a perfect solution for it that would invalidate free trade.
Like you could apply for a work visa in a lot of places as a skilled worker but it might not make sense to work there. A personal example I'll give is, I'd really like to move to Japan, I have every ability to apply for a Visa, I can even apply for a special ancestry Visa for PR. But I'm not sure I would ever want to work in Japan for a Japanese company, both because the work culture is completely backwards imo compared to western nations, pay is less than western, you have limited promotion opertunities, etc etc etc.
So Japan has a labor shortage and peoplle are concerned that immigration will cause it to turn into Baltimore maryland or something. And I kind of don't believe that because the places that have shortages require technical skills, you aren't getting a work visa to go work at seven eleven or family mart in Japan.
Another example is Italy which is a beautiful country, again skilled workers get educated using their state funded universities and programs and then leave for Germany or America or wherever.
tl;dr idk I'm just rambling about globalism