I wouldn't discount the role of tightening US immigration policy either. Starting with the last administration H-1B admissions plummeted: processing times and rejection rates skyrocketed. It's now dicier than ever to come to the US on a H-1B visa.

And despite rhetoric to the contrary the current administration seems intent on upholding these changes - processing for H-1Bs is still nowhere near historical norms.

It used to be that major tech cos would "park" people in Canada to wait for their US visas to clear. I suspect these changes are causing companies to rethink the "wait for US visas" part of the sentence. The more people FAANG parks in Canadian cities the more we will see FAANG-type compensation in those cities.

And it’s not just FAANG. Silicon Valley seems to have discovered that Canadian universities churn out a lot of skilled graduates - many who come from third countries via generous student visas. Many valley based startups have opened offices in Vancouver, Toronto, etc. and are paying great salaries not much removed from valley pay levels.

How does the exchange rate and tax rate differences affect the take-home pay comparison?

The exchange rate isn't much of a factor - since you're paying for goods in CAD$ anyway and purchasing power isn't hugely different. Some categories are considerably more expensive, like your internet bill, but for most people (and at the incomes in consideration) it's a rounding error.

Tax rate-wise (at the range of incomes we're talking about, which is to say mid 6-figures) you'd compare favorably to income-taxed states like CA, NY, or NJ. In particular whole categories of spending either go away or are greatly reduced due to the presence of things like universal healthcare, which adds to the competitiveness of disposable income. When I lived in NY I did a quick modeling of what my taxes would be like for the equivalent income in Canada and it shook out to basically even.

In comparison to no income tax states like TX the situation is considerably less favorable, though depending on your life situation there might be factors that nudge you in Canada's favor (high healthcare spend, high private education spend, high college tuition spend, etc.)