Just to be clear, you are posting this as a buyer, right?
Because sellers do not pay sales taxes, buyers do.
As sellers we will still be paying eBay/MP fees on our customer's entire payment.
So, just as we do now for US buyers who pay Internet(state) sales taxes, our fees will be based on selling price, optional eBay fees (like Promoted Listing), shipping price, and sales taxes.
For a $100 sale, to an Albertan (5%) , at the Collectibles rate of 12.9% that would be an additional cost to the seller of 65c.
For the same sale to an BC resident (13%) that would be $1.67.