Well, since this thread is under "Bank of Canada", I would have to say my favourite BofC note is the 1975 $50. I guess partly because the multicolour series was in circulation from my earliest memory until my early teens. But mostly I love this note for the RCMP image on the back and the vibrant red colour.
However when considering all Canadian banknotes, I would have to choose the 1912 $5 "Train" note. First for the nice train image on the front, and second because of the striking blue colour (unusual for that era). Plus, I believe this would be the only Canadian note that didn't have a portrait on it (e.g. of a Royal Family member or a Governor General).