It worked, for instance the 3 new stations in Laval were over budget (that's Mtl style) but the cost per kilometer was very good compare to larger systems.
If you read the enquiry into it being overbudget, it wasn't so much that the work cost too much, but the budget was grossly, if not criminally, underestimated ... likely to get the work funded. Yes, it's going to be cheaper ... as they only need one tunnel with the narrow trains, and that they are tunnelling in consolidated relatively low permeability materials, as compared to Toronto where they tunnel in unconsolidated high permeability materials. I've heard it said that in Montreal they tend to try and go deeper, to get into this material, to save money; Toronto doesn't have this option, as the geology is so different.
Also, the budget numbers are difficult to compare to other systems, as Montreal did not add any rolling stock, garage space, maintenance capabilities, as part of the extension. Even some of the station construction costs, seemed to be part of different budgets.
The trains are a bit longer to compensate for the width, they are 500 feet long, that is why the entrances in the stations alternate along the length of the train.
I believe that's almost exactly the same length as the Toronto platforms, which put 450 foot trains on 500 foot platforms - and the same length of the Toronto trains if the 50 foot 7th car is added.
The capacity is 160 passengers per car (really packed), and there is 9 cars per train, and the new train will allow a few more people where the train join, just like the new concept on the Toronto cars.
I wonder how that compares to the Toronto capacity of trains, I haven't been able to calculate it.
Probably easiest thing to do is scale it based on the area of the train. Their cars are 2.5 metres wide and 16.9 metres long. 9 of these cars would be about 380 square metres. Our cars are 22.9 metres long and 3.1 metres wide; 6 of these cars would be 425 square metres; adding the 7th car would bring it to about 473 square metres. Of course, there's details regarding cabs, doors, seating, etc. but that should ballpark it.