I wouldn't worry too much about Visas for Canadians, especially if you have a Bachelor's or higher in tech. I think there are several different strategies that can work to get a Visa. (This is coming from someone who was once denied a TN Visa at the US border.)

I think a B2 is good for six months; that's what I was planning to seek if our team was ever accepted, and I haven't had a problem getting them in the past whenever I traveled south on business. Of course, I would still be very interested to hear from any successful YC teams from Canada.