I always thought that you could until last year when I inquired for a friend. I was told that although those passes are valid when you use them, they cannot be upgraded if not bought from wdw themselves.
I had told them that I was under the assumption that any unused passes can be upgraded at any time...They said no. So I didn't think this was correct so when we went on our next trip, I went to the DTD guest relations location and asked again. They said the same thing. But they did tell me that they cannot be sure until they see the ticket/pass. So, I thought that was not at all helpful. So I had my friend call in and give them the info over the phone and she was told no.
So I'm not really sure, myself. I think the best thing to do is inquire over email and ask them to email the answer. That way if they say, yes...you have some type of proof. I think you should make sure you explain where you bought it and be clear that it's from a Canadian
Disney Store...I'm not sure if that makes any difference, but it wouldn't hurt to include it.
By the way, my friend decided to use the passes as is. She recently bought her tickets online. She wanted a 10 day pass.
Sorry, this went too long. Good luck.