As a Canadian, the best way to buy black powder is to order a case from a distributor in the states. They can't ship accross the border, but if you use one of the mailing depots just accross the border, use their address and your name. When it comes in you go pick it up & bring it accross the border yourself. Black powder is not a restricted product. There will be a small handling fee by the depot, but as a U.S. product, there is no duty. You do have to pay GST, but if you pick it up as you are returning from a stay in the US, you don't even have to pay that if it's part of your personal exemption.
I realize not all of us live close enough to the border to make this work, but surely you know somebody...... There is a limit to how much an individual can bring accross at once, but you don't have to pay Cabela's price.
Paul