Contact the seller. There is a button on the listing somewhere and a more obvious one on the right side of his feedback page.
Ask if the email/Paypal address you were sending to is correct and if the card has expired.
Make sure the seller understands your dilemma. After four days, he can open an Unpaid Item Dispute.
Oh! Does the seller actually sell to Canada? Is there a specific shipping price for Canada? If not, that's your problem. The seller will either have to send you a new Paypal invoice (including the title and listing number) or send a Mutual Cancellation if he does not want to bother with International sales.