You work at AMZN - I work at a US company in Canada too. Canada is a nation of branch-offices, largely because we have no VC-ecosystem, which is largely because we're a highly redistributive country with high capital gains taxes.
What makes us attractive for branch offices is that smart, hard-working, well-educated immigrants who can't make it into the US can often make it into Canada. Native born Canadians, OTOH, are leaving in droves (https://www.theglobeandmail.com/business/technology/article-...)
But we're a terrible place to start a company and exit, which is why it doesn't happen very often.
The original poster claimed that Canada could replace Silicon Valley - that's not going to happen without a better ecosystem for funding start-ups and rewarding founders.
As for those devs who choose to stay here when they could leave on a TN-1, make twice the money in the US after taxes and expenses (including health insurance and private schooling for kids), and work on more interesting problems at US companies, I encourage them to do the math. They're not doing themselves any favors living in unliveably-expensive cities earning pennies and not saving for retirement, and retirement will come a lot sooner than they think.
I lived in Seattle and enjoyed it, but staying in America long term was never an option for me. There's so much more to living in Canada than just our immigration system.
Even with the pay cut for being in Canada, and even with the additional taxes, I still make enough money to not need to worry about money. More money would be nice, but it's not all that motivating.
Meanwhile, those taxes go to things I think are important: a strong public education system; a health care system based on need, not wealth; a safe, gun-free society; a safe haven for refugees in need.
In my office in Toronto, probably 1000+ Amazon devs could transfer to an American office and make more money. But we don't. The same goes for the even larger Vancouver office.
Our immigration rules are just one aspect of why devs live here.