Ignore the eBay instructions and contact the seller.
Apologize for the error and tell him you do want to buy.
He should be able to cancel whatever is going on.
Except.
Does he actually ship to Canada? Was there a shipping fee specifically for Canada on the listing?
There is a Shipping and Handling tab. Look there.
If the seller does not give a specific fee for shipping to a destination, he doesn't want to sell there. Which may be the start of your problem.
So Contact Seller and ask him.
Or is this a GlobalShipping Program question?
Does the listing, viewed on a laptop or desktop,* show these words
Customs services and international tracking provided
If so, duty and sales tax on any purchase over $20 is being paid before your seller will ship. Also a $5 or so 'service charge' from Pitney Bowes who run the GSP for eBay.
*Mobiles don't show this . Yes, we think it's stupid too.