Interesting that this only applies to bullion (pure metals) and not to coins (usually alloys).
For the record, the only eBay sites that use the Global Shipping Program are the USA and the UK, so you won't have to deal with it from any other country.
Since the GSP doesn't want to change their stance, the only out is to ask US or UK sellers to ship directly and to pay applicable sales taxes and Canada Post service fees on your doorstep.
The seller is not required to do this.
It may help if you can point him to a service that includes Confirmation of Delivery or tracking.