Canada is a fantastic place - I've been all over and would recommend the following places:
Ottawa - lovely city, the Capital and definitely worth a visit.
Montreal - very interesting, you can try out your French
Toronto - worth a visit for big city buzz (kind of like New York)
Calgary - cowboy country if you fancy seeing a rodeo!
The Rockies - unmissable - Banff and Jasper National Parks (especially Banff) are spectacular - I would particulary recommend seeing the Athabascar Glacier and the Athabasca river which cuts its way through deep gorges - amazing. Also a pretty good chance of seeing a moose, and maybe even a bear.
Vancouver - my favourite city in Canada - has a real villagy bohemian feel to it - great city to just wander around, lovely beaches, interesting bars, restaurants, sites, lovely parks, an interesting port - its got everything!
I hope you decide to go - if you do I'm sure you'll have a fantastic time.