You're in for a treat at this time of year. The Christmas lights downtown are so pretty at night...
Along a fitness line...would you consider going skiing? There are many ski centres within an hour's driving distance of Montreal. On Mount Royal you can get a terrific view of the city (it's a mountain in the middle of the city, you can't miss it - just walk uphill!), and at Beaver Lake you can skate, and as well I've gone sliding with friends down a hill with cheap Crazy Carpets (The Kid in me)!
Montreal is a place to try foods of all nationalities. One place i like is the Nil Bleu (Blue Nile), a terfific Ethiopian restaurant on 3706 St. Denis. Tel: 285-4628
Le Taj has some great indian food 2077 Stanley Tel 845-9015
Here's a great site on Montreal Restaurants. There are lots of reviews. Select 'Downtown' in the Area section, as well as the price range and cuisine you're looking for. There are thousands of restaurants in this city (no kidding).
Here's a tip - save the downtown shopping for COLD days you don't want to spend much time outside! All the malls are linked underground, so you never have to venture out of doors!
While in Old Montreal, you should see Notre Dame Cathedral. The stained glass is breathtaking. Take a horse and buggy ride dwon the old cobblestone streets, and get a nice tour of the old city.
Enjoy your trip! If you're into museums and such, there are plenty around, and I'm sure you can get the information at your hotel.
Bienvenue a Montreal! (Welcome to Montreal!)