Taxi Champlain appears to be the company with the most cars around Montreal. There was almost always a Champlain car at my hotel and if you needed to call for one, the driver was there in less than 5 minutes.
The Champlain drivers were courteous, helpful with loading suitcases and knew their way around very well. They also all spoke English as one of the taxis I took in the rain ended up being something else with a driver who not only did not understand English but was rude.
Cars were clean and are mainly Buick Allures and Toyota Camrys. They also have brand new Siennas for groups of 4+