Any US broker should allow you to trade Toronto listed stocks. Fidelity, Schwab, and E*Tard.
TD Waterhouse, CIBC World Markets, and RBC are all Canadian.
If you're thinking about investing in tar sands I would do more research before you pull the trigger. It turns out the tar sands aren't quite as great as Boone Pickens thinks they are:
http://www.energyandcapital.com/article ... ak+oil/499