Well here goes:
First of all, your one essential supply: A city bus pass. I suggest buying the "CAM Hebdo" pass, its good for a week, cost $14, and offers unlimited bus/metro rides during that period. Best way to get around town is by bus/metro
Day 1 - Downtown Montreal
Here you are, right at the centre of Canada's seciond largest city. The best place to begin a walking tour of Downtown is in my opinions at the corner of Peel Street and Saint Catherine. Behind you rises Mount royal and in front of you, the land gently sinks down towards the Saint Lawrence. Walk south (towards the river) for a block until you reach Canada Place and the Queen Mary of the World Cathedral. Here you'll see Montreal in a nutshell: A church, old, turn of the century building, and modern glass towers. you can then stroll west on Rene Levesque till you reach Place Ville Marie (The large, cross-shaped building). Walk north across the plaza, and you'll find yourself on McGill College Avenue, which is in my opinion the most beautiful street in downtown. Be sure to take some photos of yourself next to the "Illuminated crowd" sculpture. Walk noth to McGill University, and have a look around if you wish, the campus is beautiful. Walk back south and visit the Underground City by entering Place Montreal Trust. It's a huge network of inter-connected shopping malls underground. Of course no visit here would be complete without a ride on the Metro (not recommended during rush hour). It's clean, quiet, and runs of rubber tires like your car. This of course is just a basic, quick overview of downtown, which is best explored as you see fit. it's almost imposible to get lost.
Stop for a bite to eat at Schwartz's deli on St. Lawrence Blvd (a little bit north of downtown close to Metro station Sherbrooke).Try the local specialty, smoked meat, which is simply incredible. I could eat here everyday!
Day 2 - Old Montreal
Take the Metro to Champ De Mars (Orange line) and follow the signs to city hall which is a great starting point for a visit around here. you'll find yourself in the heart of the old city (most of which dates back to the 1800's, you'llfeel like your in paris at some points). Walk down Place Jacques Cartier to the Old Port. Things to see include the Clock Tower, the iSci Centre/Imax Theatre, and the jet boats for the rapids (FUN FUN FUN). If you visit here on Canada Day, you'll find Mounties in full dress uniform and on horseback1 Be sure to wander a few blocks west and visit Notre Dame, which is one of the most beautiful churches in the world, I guarantee you'll be speechless at the beauty of the interior. you can also grab a horse drawn carriage ride at the square outside. any of the local cafes are great for lunch although I prefer a cheeseburger at Harvey's at Place Jacques Cartier.
Day 3- Olympic Stadium/Botanical Gardens
This will take a whole day easily. Take the Metro green line to Pie-IX and exit onto the street, walk into the Olympic Park from here and you'll great some great photo ops. Walk to the base of the tower and buy the "Get An Eyefull" package which include tickets to the top of the tower, the Biodome (a living museum next to the tower, just amazing), The Botanical Gardens, and Insectarium (full of creepy crawlies). The ride to the top of the tower if fun and the view cannot be beat. also sign up for a tour of the complex and be sure to buy Expos baseball tickets to enjoy the evening. The best seats cost only $35. Be sure to buy a hot dog and bowl of poutine during the game, yum yum.
Day 4- Mount Royal
Lots of walking to be done here, so if someone thinks they can't conquer the mountain tell them to stay in the hotel. The views from the top of Mount Royal are breath-taking. I prefer to walk up Peel street to the mountain then taking the paths to the top. This walk is tough and draining. if you can't handle it, you can take a bus to the top. Be sure to visit Beaver Lake, the downtown and East-end lookouts, the chalet, and the cross. you can spend the whoel day wandering these paths and you will forget you are at the very centre of a major city. Afterwards, take a bus over to Cote Des Neiges street and dine at Maison Kam, the best Chinese food I have ever had ( personal favs are: salt and pepper squid, cantonese chow-mein, and the beef in oyster sauce. Their won-ton soup is great too).
Day 5- Whatever you want
You can stop by one of the many festivals. The jazz festival is great! Or visit the La Ronde amusement park/ Ile Saint Helen, or Saint Joseph's Oratory. maybe even go to the botanical gardens as you really need a whole day to explore their beauty and peacefulness.
That's all I can think of for now. if you want more info about anything (i.e. directions) just ask. It's getting late, so I'm turning in. Maybe I'll post some pics tomorrow. Hope this is all helpful!