There are many different ways you can get to Montreal by car so I can't list all of them. I can, on the other hand, list the major autoroutes (highways) that go to Montreal and its bridges. Since Montreal is on an island, you'll have to cross a bridge at some point (or go through a tunnel). You can use the Google map above to move the map around or zoom on it and get all the details. The main bridges that link the south and west shore to the island are :
The Jacques-Cartier bridge : this is Montreal's most beautiful bridge and the best way to see Montreal when you come in, especially at sunrise or sunset (although sometimes - in winter that is - sunrise coincides with the morning rush hour). Be careful though, the central lane of the bridge changes direction depending on the time of day (it's north bound during morning rush hour and south bound during the evening rush hour), so check out the lights above the middle lane to see if it's OK to use it. Route 134 (AKA Taschereau boulevard) will get you to the Jacques-Cartier bridge, which can be accessed through either route 116, autoroute 10 (AKA the Eastern Townships highway or the autoroute des Cantons-de-l'Est) or the 15. If you are coming from the US, Highway 87 and highway 11 turns into autoroute 15 in Quebec and highway 89 turns into the 133 (which intersects with the 10).
The Champlain bridge : autoroute 10 will get you to the bridge.
The Victoria bridge : route 112 will get you to the Victoria bridge and can be accessed the same way as the Jacques-Cartier bridge. But this bridge only has one lane so it's not the best point of entry.
Hippolyte-Lafontaine pont-tunnel (bridge - tunnel), it's a bridge? it's a tunnel? it's both. If you come in from the south shore, it's first a bridge over part of the St-Laurent river then it goes under the river (that's the tunnel part which is actually a large concrete tube sitting at the bottom of the river). To get to the pont-tunnel, you use autoroute 20 and you can take the Sherbrooke (route 138) west exit to go downtown once your are on the other side.
All these bridges and autoroutes are busy (to say the least) during rush hour. Also, the Jacques-Cartier bridge is closed for a couple of hours for the fireworks during the summer competition either on Saturday or Wednesday nights usually from 20:00 to 23:00.
If you come from the west, you can take either the 40 (AKA the Trans-Canada Highway known as the 17 or 417 in Ontario), you'll then cross the Ile-aux-Tourtes bridge, or the 20 (known as the 401 in Ontario) then you'll cross two little bridges (you won't even notice them).