How is this possible?

[Prince of China]

At the www.ebgames.com website, it says that all prices are shown in U.S. dollars and that Prince of Persia: Warrior Within is $49.99(USD). But at www.futureshop.ca, it says that Prince of Persia: Warrior Within is $49.99 CDN. I thought that manufacturers set up a price that retailers had to follow. What happened here? Why is Electronic Boutique selling Warrior Within for a more expensive price?
I guess I'll have to trade in my games plus the additional $50 I earned thanks to my report card.