Maybe there are risks we don't know about or understand with doing business across international lines.
Certainly there may be tariffs on some categories of trade goods, maybe one of them is books, fiction books or something.
Maybe the companies have more liability when shipping to Canada given the different legal system.
Perhaps there are some extra fees they have to pay for the purchase of a license to do business in Canada that they pass on to their Canadian customers.
I have not run a business selling items from US publishers to Canadians in Canada but I can only imagine that there are some laws on the books that Canada uses to encourage Canadians to purchase things from Canadian publishers and to spend their Canadian dollars inside Canada.
All countries stack laws in favor of their own native businesses. Please don't take the following as a political commentary, but I'd wager a country that is more left leaning and socialist as Canada is , unless I am mistaken, does it a lot more than some more free market economies.
This is a complex international business decision motivated by the desire to make money as is the bottom line with all companies that do business anywhere.
International business is a multi-faceted and highly complex thing with variables unique to not only each type of business but each specific company, product and even each separate contract within the same company based upon the existing laws at the time of its origin.
I would highly doubt that a company is charging Canadians more as some sort of plot to limit access to gaming materials or to exploit the Canadian customers through deceptive exchange rates and trade practices.
I think they probably just have to pass on some of the higher costs of doing business internationally to the customers who reap the rewards and benefits of their products availability outside the boundaries of their home base, which is in this case the wonderful country of the United States of America.
Food for thought...
DH