Pay as you go broadband isn't that popular here in the US/Canada (at least, that I'm aware). It looks like Virgin Mobile has such a thing, but the set-up cost (150$) is rather high.

I would more likely try to get a wifi package from AT&T, Boingo, iPass, etc. It's not perfect as you need to find a wifi hotspot, but it's manageable and much cheaper than Virgin Mobile.

One thing that I've noticed is that US companies are much LESS likely to have programs that includes Canada, versus the opposite. Seems like Canadians travel a lot more to the US versus Americans to Canada.

HTSC