Montreal can get quite cold in september, but doubtful you'd ever snow.
Generally speaking, after the beginning of september, it gets chilly enough that you need a jacket (spring type, not winter jacket) whenever outside.
I wouldn't suggest going past the end of september if you get chilly easily. I would rather consider mid-august to early september.
JP
Originally Posted by
BiziBB
What times or dates at either end of summer do you recommend? We'd try to have a day and night here, maybe in early September '08.