I have the same problem (I am also in Canada). None of the stores accept coupon printed online. Wal-Mart cashier has the worse attitude and told me they don't accept "Home-made coupon". Just sounds like I am using counterfeit coupon.
I have visited numbers of stores (Wal-Mart / Metro / Shopper's Drug Mart / Loblaw) in my area (Canada - Ontario) and none of them accepted the printed coupon. How can I receive coupon that can be used?
