Let's consider where they want to build Metro interchanges.
Gare Centrale already connects to multiple Metro stations in the dense downtown Underground City, so no work required here at all, really.
Édouard-Montpetit was actually designed to one day connect to the tunnel when it was built; new shafts would have to be dug, but I understand there are no utilities in the way.
McGill would need the most work, as a connection was not pre-designed. But we only need new pedestrian links, which can be built in a more flexible manner than rail tunnels (which, once again, already exist).
Other connections would be with the commuter rail system, not the Metro, and are even easier to build.
Gare Centrale already connects to multiple Metro stations in the dense downtown Underground City, so no work required here at all, really.
Édouard-Montpetit was actually designed to one day connect to the tunnel when it was built; new shafts would have to be dug, but I understand there are no utilities in the way.
McGill would need the most work, as a connection was not pre-designed. But we only need new pedestrian links, which can be built in a more flexible manner than rail tunnels (which, once again, already exist).
Other connections would be with the commuter rail system, not the Metro, and are even easier to build.