I didn't actually want to leave, but I was staring at the prospect of not unemployment, but underemployment.
Canadian industry doesn't really that many companies that can absorb Ph.Ds. It's not a money issue -- I was willing to accept Canadian pay. This was ca 2010s, and there were very few homegrown Canadian companies that had enough scale to need high level R&D (this was before Shopify and the rest). It was either you did your own startup and found your own funding or you worked entry level engineering jobs doing things like testing or audit work.
All the design and original engineering work happened at HQ in the US or Europe -- the Canadian office is usually just a branch office.
In the US, it's analogous to Chicago offices of big tech firms. They're just marketing and sales offices -- the real engineering work happened on the coasts (SF/Seattle or NYC).
So I reluctantly left Canada for a US company that although not famous, had a global footprint. Whatever I worked on immediatley had global impact because engineering was done in the US office and replicated worldwide. I learned a lot about how to operate at scale and over international markets.
Canada is a small country that has an education system that punches above its weight -- Canadian schools are excellent. But it has an industry that unfortunately doesn't. Somehow Canada has tried and failed a few times, with Nortel, with Blackberry, etc. to develop champions. Something is preventing Canadian companies from scaling. Even far smaller countries like Sweden have companies that are global (IKEA, Saab, Volvo etc), so I'm not sure why we can't do it too.
Maybe the old saying that Canadians are "hewers of wood and drawers of water" has some truth -- it's easier to extract resources than to compete on differentiated product.