Lots of 2020 planning going on in my office, and this question came up, at what point does frequent USA travel for work necessitate a work visa? Like if you were down for a week a month? Or half the year, or what? What's the dividing line? Does it matter which side of the border is paying you?
I'm sure there's a government website that lays it all out, but I find the answers from you beyond.ca nerds more amusing, so I'm not going to look.