Some sellers, particularly new ones, were signed up for the Global Shipping Program without realizing it.
It is a comment on the importance of the Canadian market to US sellers, that a year after the practice was dropped some of those sellers are getting their first Canadian sales.
Ask the seller if he will sell to Canada. Tell him that he can opt out of the GSP. Tell him that he can ship to Canadian buyers directly using USPS First Class International and will still have Confirmation of Delivery, which is what a lot of sellers really want when they agree to the GSP>