The list of Canadian mail order fruit tree sources so far:
Alberta Nursery and Seeds - Mostly smaller fruits, bushes etc., great prices
Corn Hill Nursery - Small fruit bushes, maybe heritage apples (they sell 'm but not mail order)
Denman Heritage Apple Trees - Good selection of apples/pears, but they are zone 7, so beware!!
Dominion Seed House - Some fruit trees, including Asian pears
Green Barn Nursery - Rare cold hardy fruit trees, asian pears, apples, plums, very expensive!
Grimo Nut - Great selection of nut trees, good prices
McFayden - Large selection of berry plants and a few trees
Mr. V's - Nice selection, though often sold out, prices on the high end.
Rhora's - Nut trees and a few other items
Siloam Orchards - Heirloom apple and pears (and a few other items)
T & T Seeds Ltd - Good source for U. of Saskatchewan cherries, good prices too!
(Siloam Orchards have a staggeringly broad collection of apples for every use).