Welcome to Montreal.
Mr. Janczuk has some excellent advice, with one caveat; go investigate dojos for yourself and see what appeals to you
With that in mind...
1 - There used to be an aikido dojo on St-Charles boulevard, but they closed down. I believe they re-opened in Hudson. I have no idea who is teaching or what they are like.
2 - Mr. Andrew Darnel is currently running classes in Ste-Anne-de-Bellevue. I have had the pleasure of practicing with him on several occasions and can say he is a fine martial artist and genteman, though I have never attended one of his classes. Perhaps you and I could meet and try them together? Details = http://www.abcmontreal.ca/
Anything I can help with just ask, and good luck.