A good way to search for stores is
Inkmesh. What you are looking for is Adobe Digital Editions ePub, which is the format supported by most reading devices except the Kindle. This has DRM (encryption), but see
Adobe ADEPT DRM for EPUB circumvented. Don't buy from Barnes and Noble, because they don't use Adobe DRM on their ebooks. It is my understanding that there is no law against stripping DRM for personal use in Canada. Once DRM-free, Calibre can convert ePub to MOBI for your Kindle.
The last issue is geographic restrictions, which is why Amazon won't sell you the US ebook. You will have to spoof the selling site to some degree in order to convince them you are buying from the US. How to do this is something of a moving target, but see for example
If only I lived in the US.