It's not a Canadian issue. It is a stock issue. Those in the US trying to get upgraded bands get the same error message. There have been previous threads dealing with this exact issue.
Despite the fact that you can get all the way to the order page and submit your order before getting the error, be assured that if the band is actually in stock, your payment will go through. You will get an error if there is no stock despite whatever the stock page might show.
I went through the exact same thing last year trying to get upgraded bands for my trip this month. I tried religiously for 2 months to get bands and finally managed to get 3 upgraded bands and 1 regular band (had 4 upgraded bands in the cart but my order did not go through until I figured out which band was actually out of stock and swapped it out for a regular band). It was an extremely frustrating process. When I emailed Disney about the error, they told me it is a stock issue, that they were aware of it, and they were trying to fix it. That was 4 months ago - looks like nothing has changed.
For what it is worth, the stock page used to update almost every hour at the 43rd minute (I.e. 2:43, 3:43, 4:43, etc). Not sure if that is still the case.
Good luck to those trying for upgraded bands! Hope the effort pays off!