I have ordered from aquariumplants.com with good results. Not sure about Canada shipping though.
Other reputable sites:
If they ship to Canada, those are the stores I'd use.
Don't use AZ Gardens. They send the wrong plants half the time.
Another good way, which is the best way to get the HEALTHIEST plants is to become a member of planted aquarium communities, like plantedtank.net. There is a Swap and Shop section where members sell plants and clippings, and you can get nice deals there. I have to say that plants from other members are always in better health than the ones mass-grown in the shops.