Let me give you the reason that this blew my socks off. The ebook market share in the US is only about 7%, assuming that we use the AAP stats as a yardstick. That means the Canadian ebook market is growing faster than the US market. I hope you were sitting down (sorry).
This raises the obvious question, why is it growing faster?
The US market is older, and we've had Amazon pushing the Kindle since Fall 2007. I don't have specific details on the Canadian market, but I would bet that it started taking off after Shortcovers became Kobo. Kobo was owned by Indigo at the time and it was heavily promoted in their stores.
That in-store presence could have made the difference. Yes, B&N lunched the Nook at about the same time that Kobo was launched, but B&N doesn't have the market presence you might assume they have. For example, I don't have a B&N store within driving distance. (On the other hand, I do have a Books-a-Million nearby, and the value of the in-store presence might be why BAM carries the Nook.)