Montreal is a summer and fall port. It is particularly beautiful in the fall when tree leaves are changing color.
Most cruises out of Montreal are along the east coast and the vast majority of these are 7 to 14 nights long. Both roundtrip and one-way cruises are options, with the one-ways typically ending in Boston or New York.
At the end of autumn the ships leave for the season. Most of these reposition to Florida over 10+ nights.