Montreal is a great city in all four seasons (yes, there are actually all four), and each one brings new, fun and interesting things to do and see.

Winter brings the snow and the cold, but Montrealers have adapted with a number of great activities.  The "mountain", central in the city, hosts sledding, cross country skiing and snowshoeing.  A short 45-90 minute drive north, east or south of the city has several dozen ski resorts, including many small ones, but also Mt Tremblant, St. Sauveur, and Orford.  Add to that one of the highest ice rinks per capita, with almost half of the city parks setup for skaters and pick-up hockey.  Expect cold to colder spells of 10c to -20c (50f to -5f?) and snow that can drop several feet at once (but with snow crews that clear it as soon as it hits the ground - Montreal is more prepared than Toronto, Boston, NYC or Atlanta).

In the spring, the snow melts and the "mountain" is a great place to take a walk or run especially around Beaver Lake.  It is not unusual to see the early kayakers out on the river and the cycling clubs on their $5000 rigs biking in packs on the street and the Lachine Canal path to Old Montreal.  Early season (March-April) come the Cabane a Sucre (sugar shacks) where you get to try the purest maple syrup and traditional French Canadian fare. Expect weather to be 20c to -5c (65f to 20f).

Summer is festival and event time with the Jazz Festival, Canadian F1 Grand Prix, Just for Laughs, and several other internationally known events coming one after another.  Great dining and people watching at night on St. Laurent or St. Denis and the European flair of the city brings many back over and over again.  The lakes in the region make for great get-aways no matter what direction you travel.  Temps are warmer, 25c to 7c (80f to 45f).

Fall brings the leaves changing colors all over the city, as well as the retreat back indoors, where Montreal hospitality shines.  The underground city connects a number of shopping, dining and entertainment areas where you can spend seemingly weeks without having to see the light of day.  Enjoy the museums, restaurants and all the indoor activities.  Put on your coat for the 20c to -2c (70f to 30f) weather as the season wears on.

Based on the type of person you are and your tolerance to weather, there is surely something for you in any season.