If you want to cancel the order, you will have to ask the seller to send you a Request for Cancellation, which you will quickly respond to accept when it appears in your messages.
However, the seller ships worldwide but simply has not specified shipping to Canada, so whilst it is always best to ask in advance of buying, the seller can send you an invoice with the shipping charges, whereupon you simply pay from your Purchase History like usual. There should be a Request total from seller link at the check-out when you try to buy, or you can send a note to the seller yourself with the request.
