It is my experience if you need to buy prescription drugs in Canada, you will need a licensed Canadian physician to sign the script. On my trips to Alaska, I fill them before I go and if I stay long enough in Alaska, will have them filled there as I use Walgreens for the most part. On a couple of trips, while in Canada I have needed some prescription meds, I have stopped at one of the walk in clinics, such as in the Edmonton Mall and have seen a Canadian doctor. Then it is a matter of walking next door to fill the script. The only problem I have ever had was the clinic, figuring out how to charge me since I don't have a provincial medical card and number. LOL
The last time, they decided that $35 by check was fine and I was off to get my meds.
One of my physicians here in Florida is a Canadian citizen and is licensed to practice medicine, here, as well as in Canada where he was educated and became a physician. He will write me script to take with me, if I ask for it.
But for the most part, I get three month fills before going and that will last most trips. My current prime care physician will also give me extra script on paper to take with, in case I need to get a refill on the trip somewhere. Since I don't take anything too unusual, mainly blood pressure pills, it doesn't give her any reason for concern. She is also willing to double the size of the pill, then I cut it in half, effectively giving me a 6 month supply. In the long run it costs my insurance company less as the larger dosages are usually just a few dollars more than the lower doses.