For quite a while Kindles were not available internationally, and that included Canada. The main sticking point was the 3G wireless support for Whispernet. Eventually Amazon inked deals with several international carriers and started selling the Kindles worldwide. This included Canada.
However, Kindles are still not available from amazon.ca, the Canadian amazon affiliate. Any Kindles ordered from amazon are sold by amazon.com and shipped internationally. A small distinction, but it can be important under certain circumstances.
At the current time, Kindles available to the Canadian market lag significantly behind the American market. The Kindle Paperwhite is not available here. As the Nook Simple Touch with Glowlight is also not available in Canada, it leaves the Kobo Glo with the front-lit e-reader market all to itself.
As near as I can find the Amazon Fire is not now nor has it ever been available in Canada. In its place is the Kobo Arc and several other Android tablets that are not specifically marketed as e-readers.
As for the book selection: research on the web suggests that not all Kindle books are available in Canada. However due to the massive amount of ebooks out there it's difficult to confirm or deny this. Certainly books from the main "Big Six" publishers are available.