A deactivated firearm is not considered a firearm; however, it may, in some circumstances cause you legal trouble since good dewats are hard to tell from working firearms. Quebec police tend to be fairly rigid about enforcement and it is easiest to have the paperwork even when it is a dewat. Did you do a google search such as "firearm, dewat or deactivated,(or replica) Montreal? You might try some of the Montreal area Firearm Stores, particularly military ones. Ones I know of in Canada that supply dewats include Marstar, The Soldier Shop, and the Kenogami Gunshop. There are others but perhaps a quick google search will bring up what you need.
Sometimes hunter safety examiners also have access to deactivated training firearms, including Lee-Enfields for their courses.
That's where I'd start anyway.