Did you message the buyer after trying to send the invoice to ask if they have a US or Canadian address?
Sometimes people from other countries have an address in Canada or the USA. Either a friend or family member. Or a forwarding service. It happens all the time. Their profile is still attached to whatever country they are in, but when they go to pay for your item they will enter their US/Canadian address.
If you didn't contact them. this might be why they are confused and think you "made up" the story about the not having a Canada/USA address.
The actual way to resolve the issue would be to contact the buyer and explain why you thought they weren't in Canada or USA, ask if they have an address in one of those countries, and then re-list the item for them as a Buy It Now that requires immediate payment. Ask that after the item is shipped, they accept a feedback revision on their original negative feedback that was clearly a misunderstanding between you two.
eBay is unlikely to remove the feedback because if you never even contacted the buyer to ask them about the problem, to them it looks like you cancelled an auction for an invalid reason.
One negative feedback also doesn't matter much so long as your reply makes you sound professional and easy to deal with.
