It may not be the best depending on your area, but you can sign up for Sprint EPRP (kind of like employees friends and family). You can find it
www.sprint.com/SERO I believe it runs $59.99 for 500 minutes plus unlimited text and web. Plus, its not always possible but I was able to add a corporate discount to that lowering it further. As for usage in Canada, I'm not sure how heavy your usage is, but I use separate services (i.e. calling cards, and forwarding numbers) when I'm calling internationally. Another option is to pick up a cheap GSM phone (1saleaday.com has them all the time for under $100) and just buy/rent a local sim card when you're in Canada.
Not perfect, but I hope it gives you something to consider.
