But I don't think anyone is willing to go to Canada considering the huge salary gap. I got Canadian developer friends who is making half of what I am making in US by sheer number besides the currency exchange rate.
I don't know where you live in the USA so I cannot really judge but I think you should also take in consideration the cost of life in USA and Canada. It's not only about how much you make but about how much you spend.
However, this does not adjust for free healthcare and education.
On the other hand, tech cost of living is skewed by SF and Vancouver.
SF is the #1 tech city in the US whereas Vancouver may be #2 in Canada, but the US is a larger country so SF may "dilute" more. Without stats, this is just guesswork.
I feel like if you are at the top of your game, and can make it at any of the major tech companies or can start your own startup without trouble at finding funding, the U.S. is way better. Most of my friends, including myself, earned 1.5-3x what we'd earn even in a major city as Toronto.
And if you happen to join a great tech company, chances are the health insurance you'll get is superior to the general public healthcare system in Canada.
California vs Montreal is cherry picking the data. You could easily say Chicago (cheap) vs Vancouver (not cheap).
The major economic tech centres in Canada are Toronto and less so, Vancouver. Montreal and Ottawa (because that's where Shopify is HQ'd) are the next biggest.
Toronto and Vancouver are hugely unaffordable when it comes to housing; Montreal and Ottawa are much more affordable.
On the flipside, Vancouver is apparently more expensive than anywhere in the US for housing and median salary is much lower than somewhere like New York City.
Montreal is a big city, so I concede you have a (partial?) point. I have heard horror stories about cost of living in Vancouver here on HN, as well as from people I met in real life.
I'm not sure the gap is that big when you factor in children and housing.
I have two kids. I get offers between 100k/160k CAD in Montreal. Daycare costs me about 800$ per month for each children and I get kick backs from the governement to bring that down to roughly 189$CAD/month. In San Francisco the average is 1900$USD per child.
Then factor in I live in a 265K CAD house, 40 minutes bus ride to city center. I have 3 bedrooms, one office, a huge kitchen, a nice patio, garden etc... In San Francisco the median house price is 1,194,300$ USD.
I could be making 180kUSD and I wouldn't be saving any more money at the end of every month with housing and daycare alone.
Also... I might pay a good deal of taxes but I have great healthcare.
The USA is not defined by Silicon Valley. I make 120k in Richmond, Virginia and another 30k online. Your figures are nowhere near accurate for most American cities.
There are other reasons than money one might live in Canada. It's a country with different values than those of the US. Welcoming to immigrants, relatively safer in terms of violent crime and universal healthcare are high on the list.