Actually this is available for anyone who wants cheaper medications. There are a ton of these sites around. You have to provide a legitimate prescription (some that I saw wouldn't take scripts for controlled meds) which is reviewed by a Canadian doctor who would write his own Canadian prescription and send it to the pharmacy, who would send it to the customer.

[edit] Here is an excerpt from the site Canadapharmacy.com:

How to order Prescription Drugs:

Choose items and place them in your shopping cart.
When you checkout you will be asked to create an account and fill out a brief patient profile.
Follow the steps to complete your purchase.
Fax or mail the prescription from your Doctor and also a piece of a picture ID (Driver License) to us.
Your Doctor's prescription will be reviewed and re-written by a Canadian Doctor and dispensed by our Pharmacy.

[edit]
This is from their faq page:

4. Do you sell narcotics?

No, it is illegal for a Canadian pharmacy to mail a narcotic or controlled substance to a US resident.