Contact the seller and apologize for not reading the listing completely.
Ask for a shipping price to Canada. Be prepared for a shock, shipping by USPS with Confirmed Delivery starts around $20 and goes up with weight and value.
If the transaction looks to be outside yourbudget, or if the seller really does not want to ship here, ask politely for a Mutual Cancellation. When this is sent, accept it promptly. This will release both of you from the transaction.