Not to break into the Uber discussion, but the fleet of vehicles seem like a problem given the Montreal environment:
Leaf and Soul:
Battery Range is short - In the non-climate control seasons best case 200 km of slogging through traffic at low speeds. (more like 150 if you can get up to speed on an expressway)
Winter time much worse, since I don't think a passenger is going to be happy with the heat turned down. maybe 100 km.
Even with DC fast charge, it's (i seem to recall) 30 min to recharge. so every 3-4 hours (or less) the taxi is forced out of service for 30 min - not even counting travel time and km back to the Chademo plug.
Tesla Model S
Range should be OK- can probably get through most of a shift and can probably get to a supercharger over lunch
The real concern however is the potholed nasty streets, the cost of bubbled tire sidewalls (and also bent rims) may negate any fuel savings.
I guess the real issue might be when the taxi has some range, but not enough for whatever the person next in the cab requires - A little different scenario than a cab that can take 5 min to get a tank of gas.
I like electrics and may get one for my next car, but they are best suited for planned / expected routes.