You can shop worldwide online for just about any legal product - except your prescriptions. Being required to buy locally in this one instance gives the seller unique power to control the market.
There are import tariffs and restrictions on all kinds of products. You may think you've found a golden loophole, but it is foolishness to think the manufacturers are going to send enough volume of pills to Canada to have them be re-imported in the quantities Americans would need.
The price in the US is what it is. If you want Canadian prices, move to Canada.
I've done that on other products. One of the most recent was a Mozart CD collection (recommended here at FR) which was over $300 at amazon.com, but about $100 (including shipping and currency exchange rates) at amazon.de in Germany. If American consumers could buy drugs across borders, then the drug companies would have to spread their R&D costs across all their customers instead of just sticking Americans with them.
I think that many of the Dems who voted for this just want to keep current prices high to cause the collapse and ultimate nationalization of the American health care system sooner. The drug companies are feeding the aligator and hoping to be the last one eaten eith allies like that.