Here is what you have in mtl, take a look at their websites
Action500 - Paintball in Montreal & Laval - Indoor Paintball Centres | Action 500
they have 2 fields, one in mtl (CJ has been, 1 big indoor field) and one just up the road from Skorpion (its tiny, would not recommend it)
Skorpion, Skorpion Paintball - Accueil
I havent been in a while but my buddy has a membership there, they have i think 2 indoor fields and 1 outside. its ok.
Arnolds - Arnold Paintball - Paintball Intérieur Lasalle | Paintball Extérieur Hemmingford | 1-877-300-9238
, they have a indoor field in the south west side of mtl. a while back they had pump/pistol nights. I havent been in a while but I liked their single indoor field (was a fort like buiding with a courtyard)
Mirabel - Paintball Mirabel: numéro 1 au Canada | Paintball Mirabel
, they've been around for ages, they are huge and have a giant dome as their indoor field. I only played the dome once a few years back but it was nice.
There's a few more fields but they are either outside of MTL or have no indoor field.