If there is no Canadian discount or DVC discount (like the 7 days for the price of 5), your best bet is probably an authorized seller. I have purchased from Park Savers before. The discount is small, but better than nothing.
Last year, Disney had a significant discount for Canadians with non-expiring tickets. They have the same discount right now (sale will be over within the next few days) but the current tickets expire at the end of the year. Given the current exchange, Disney might run the sale again next year. It is obviously attracting Canadian guests, since they decided to run the sale again this year. I bought 3 sets of non expiring tickets last year. Should have bought more.