Did you by chance ship by surface mail? That can take months to arrive overseas and the truth of the matter is mail does go missing, not very often, but it does happen (It's happen to one of my sales to Australia).
Did you use small packet international? If so you should have $100.00 insurance coverage. Get all the info together - i.e. date of purchase, date shipped, recipient's information, package contents and value, etc. and call the 1-800 number for Canada Post. If it was small packet, since it is not a tracked service, you will not be abe to start the claim for 75 days from when you shipped the item, but you should be able to get your money back that way.
If you used surface mail, it is quite likely it is still on route. It is a bad idea to ship anything overseas by surface - always use Air because it almost never makes it to the recipient before the time limit is up to file a PayPal claim. It is quite likely that your buyer does not have the package. The only form of proof of delivery that is acceptable to PayPal is to provide them the tracking number so that they can see the package did in fact arrive. There is no way to prove your buyer actually received the package just because you delivered it to the post office - like I said, things do go missing. Set a limit for yourself as to what value you are willing to risk shipping without delivery confirmation - anything above that only ship by delivery confirmed service.
You want to avoid PayPal claims at all costs because when you lose them, it hurts you as a seller, which could likely cost you a lot more than that $90.00 in the end if you wish to continue to sell on eBay if your selling privileges get restricted. If you can't prove the buyer received the item, you are best off to refund them and then proceed with the post office claim.
BTW I have refunded people who said they did not receive their package and when the item showed up they paid me back. There are honest people out there who do things like that.
