Other than those who have left Canada for the US and a few other small circles, the preference for Canada's best talent to leave for the US and the dramatic difference in career prospects doesn't get a lot of discussion in public discourse.
I believe in part it's because doing so would force us to publicly confront the uncomfortable truth that when it comes to ambition, creativity, and grit, Canadian companies don't employ the A-team. There are exceptions, but they mostly get the B/C players. Some broad generalizations are below, but I've worked in the tech industry for 20 years across multiple US/Canadian cities and in my experience they hold up.
Broadly speaking, you can split Canadian tech worker employers into a few categories:
1) Big, noncompetitive, unambitious, staid large companies making decent money via rent extraction in the Canadian market. Often times "by Canadians, for Canadians". They're minimally innovative and have largely incremental growth prospects, but because they have pricing power over their customers they subsist by turning the screws on customers and tweaking to control costs. They don't grow productivity or produce consumer/market surplus. With a few exceptions, they don't compete abroad (either they do and they're bit players, or they don't but we know they'd get creamed).
2) Small/medium sized Canadian companies. There are some genuinely interesting ones here but honestly, most don't even theoretically have a shot at hitting really big. There are a ton of small/medium sized niches with increasing venture funding, and that's great. But they are just never going to be large or profitable enough to compete with deep-pocketed US employers for the best talent. They'll end up successfully extracting rents from a niche or become the branch office of a US company. If you listen to the Canadian business/tech press we're on the cusp of a major breakout here, but we've been undeservedly pumping this narrative for almost as long as Torontonians have been the only ones in the world pumping the city as "world-class". Is 2021 the year Hootsuite will finally become a unicorn? (spoiler: no).
3) Shopify. They're special (relative to the rest of Canada) because they're a high-growth business in a huge, scalable, global market. Unlike #1 their industry isn't protected, so they actually need to compete on merit and generally do. They're recently profitable, but not that profitable.
4) Canadian satellite offices of US tech companies (some highly profitable, some highly ambitious, and some just there for skilled labour on the cheap). They mostly skim the cream off the top of the local labour markets, paying much better than #1, #2, and usually #3. They also bring skilled talent in from abroad, particularly those with trouble clearing US immigration.
The entrepreneurial A-team generally leaves to start businesses in the US. Canada is too small for them and the environment frankly seems to clip their wings.
The non-entrepreneurial A-team will move to the US to 2-3x their salary and 10x their personal growth (since they're now surrounding themselves with the A-team), which they can do because US immigration is a non-issue for most Canadians in tech thanks to NAFTA. Or they'll stay in Canada and work for either #4 or Shopify, since those are the best jobs. This is really hard to overstate. Anecdotally, from tech people in my social/professional network, with 1 exception the best people are either in the US or work for US companies from Canada.
The B-team works for #2 (who only pays enough to attract the B-team, so it's self-fulfilling) and can still do well for themselves, but it's a very different world. Slower-moving, less excitement, less growth.
The C-team works for #1. They're the ones who work on billing systems at Bell, keep the lights on at BMO, maintain inventory management systems for Metro, or are perhaps involved with government contracting at IBM/Accenture.
#1 are highly politically influential oligopolies. #2 captures a lot of mindshare and (in)direct subsidy ("X is the next Shopify!"). Neither want Canadian tech workers to become more expensive, and they all resent having to compete with #4.
You see this once you look for it. Toronto's Amazon HQ2 bid was run by Ed Clark, former CEO of TD. Part of his pitch was that Toronto software engineers were 30% cheaper than in other markets (if you’re a software engineer who can work for Amazon, 30% is a significant underestimate). Not because of health care. Because of wages. All the while, local tech employers complained about how difficult it would be for them to compete against Amazon for talent. This got a fair bit of press and no one with voice in Canadian public life is willing to fight back. An industry and culture that complains about the presence of competition is not an industry which will stimulate the growth of competitive businesses.
So US companies continue to quietly be the first choice for Canada’s best. Everyone else makes do with what’s left behind.