This nail was first driven into eBay's coffin over four years ago and this site still seems to be lumbering along despite the nail now turning rusty.
It's important to keep in mind that the Global "Shipping" Program is actually more of a glorified forwarding service. The seller ships the item to a central-ish location in Kentucky, and the item gets shipped out to Canada (usually Mississauga) from there.
If you need confirmation that you haven't received your item yet, you can track it online at https://parceltracking.pb.com/.
As with any shipping service, it's not going to be a perfect fit for every single item available on eBay. (Express Parcel service is a lousy way to ship postcards, but people don't usually say that's the fault of Express Parcel.) What I think is often happening is that the program is being automatically applied by eBay to listings where sellers haven't provided international shipping options but also haven't blocked bids or purchases from users without US shipping addresses.
The way I see it, many items where the GSP is being used inappropriately are being offered by sellers who, in the "old days", would need to be convinced to ship to Canada. If they refused to ship to Canada, you'd have to work out how to get your item sent to a US address and sent to Canada from there. The GSP is pretty much doing the same thing, although possibly at a higher cost because its shipping costs are generally structured to be comparable to parcel post, not oversized letter mail (First Class International / Small Packet).
You're still free to set up a US shipping address and deal with forwarding items yourself if you find a GSP listing where the seller doesn't know that they're opted into the program or doesn't want to leave the perceived safety of the program and refuses to relist the item to accommodate you as a result.
As for your observation that the item is charging "brokerage" for items valued under C$20, keep in mind items have to clear customs regardless of their value. In the early days of the GSP, those "import charges" were for everyone to see, but too many eBay users seemed to be confused about why they were being charged. They're now folded into the shipping charge instead.
If you're still seeing items with selling prices of C$20 with "import charges" applied to them, either eBay is experimenting with having those charges show up on listings again, or else they're in categories where the items don't have the C$20 exemption, such as books.
