First step is to contact the seller and tell him what size of shoe you need.
Second step, if he does not have that size, is to ask him to send you a Mutual Cancellation. If he does, accept it immediately.
This will release both of you from the transaction in a friendly manner.
Be polite, because he has another option.
The other option is that the opens an Unpaid Item Dispute. If you do not pay, you get an Unpaid Item Strike on your buyer account. Many, perhaps most, sellers have automatic Blocks against bidders with Strikes.
It is important to read all parts of the listing carefully. In this case, you did not see a size, but bid anyway. Other buyers have bid without understanding that the seller will not ship to Canada, or will ship at an extremely high rate.
It takes a while to catch on to all the potential problems and avoid them.
But most people, including eBay sellers, are honest and want to help.
You catch more flies with honey than with vinegar.
Politely-- Captain Malcolm Reynolds
