I've relied on CanadaVet for as long I can remember. I learned the oddities of getting meds from Canada when you could still mail-order HUMAN drugs from there (NOT from CanadaVet, duh).
The meds came from Turkey, Italy, you name it. It freaked me out at first, but there were no problems. Cross-border mail from Canada ALWAYS takes at least two weeks. (Try ordering something from Canada on eBay -- you'll see.) I order my dog's meds a month in advance.
When I've had substituted meds, they do the same thing as what I ordered. Usually, it's the same manufacturer but a different form (liquid instead of a pill, etc.).
All this stuff is bizarre till you get used to it. If you can't, just shop local.
Reason of review: Good quality.