My understanding is that if you buy the dvds at amazon.com and have them sent to canada, there could be wonkiness at the border. So Bart has had a bunch of them printed in canada and set them up at amazon.ca. People can then get them plenty fast and without the wonkiness. It seems that a lot of people are doing this!
First, there is no difference if you by from a link or from the amazon.ca page directly, as long as this link refer to the actual amazon product sold by greenhouseprod and fullfilled by amazon. If not , that mean that somebody pirated the content and try to sell it himself. Do you want to post this link here so i can confirm with you ?
On what Paul added, if you are in Canada and you buy from the amazon.com store, then you will have to pay for shipping and amazon.com may show you or not, but you will have to pay for custom duties. Most of the time it happens at your door step, the postman will not give you your package until he collect the tax ! Not to add that Canadian customs have a tendency at holding package for couple of weeks sometimes !