Montreal is the biggest city in Quebec, and being the second metropole of Canada in term of population. It is also a well sprawled city with suburbs sprawling on about 100km in several direction from its Downtown.
Montreal is also an incontrovertible city for every travellers as all the highways and main routes goes through its urban centre, which is an island and one of the rare crossing point of the St-Lawrence. With a population over 3 millions and only few bridges, traffic jam are pretty common. It usually takes up to about an hour to cross the city from one point to another when the traffic flow is smooth and obviously certain industrial spots (especially along 'Boulevard Metropolitain' in Dorval Airport Area and along the A-40 in 'Montreal-Est') are to avoid being stucked.
Certain specific spots in the urban area, mainly nearby the metro station are well known for car-sharer and would be a perfect starts to leave the city. A sign marking the city you are heading to will always lower your waiting time, and will more surely help you getting a lift out of the island by a commuter faster.
Going South, New York, through highway A-15
You can walk North from the metro station Longueuil and find the bridge crossing the highway to join the A-15 in direction of the New-York State/USA. It's probably not 100% legal to stand on the good spot there, but you will probably quickly get a ride. Be careful at the New-York State border.