Hello 'awextpe',
Have you tried asking those sellers (GSP users) if they would be willing to ship the item to you using plain old USPS First Class?
First Class now comes tracked into Canada, and at a fraction of the cost of Priority or GSP. If you are serious about purchasing an item, the seller may be willing to change the listing to reflect the postal cost thus enabling you to buy it.
Otherwise, yes, you are correct that in its current form the Global $hipping Program is not at all good for Canadians. Many buyers see GSP in the listing and promptly find another seller. It is, however, good to keep in mind that most sellers who opted in to the program did not know how outrageous and infuriating the added costs would be to Canadians. Those charges don't show up when they view their own listings, it is only apparent on this side of the border. Another country will have a different set of numbers.
So not much we can do about it. As you say, the costs make buying prohibitive, and worse - it is very difficult to get those charges back in the event of a return. It's up to you to get the best value for your money, whether that means finding an accommodating seller or waiting until a more affordable copy of the item comes available.
Happy shopping!