Police say they received a tip about the alleged heist and arrested three suspects, aged 62, 63 and 65, on Friday.
Montreal police Const. Daniel Lacoursiere says a series of raids were carried out after that.
He says detectives swooping in on one apartment late Saturday found what appeared to be an explosive device.
The building's 40 residents were ordered out while tactical squad officers figured out how to defuse the device.
They destroyed in it a controlled explosion early Sunday morning.
Lacoursiere says the three suspects will face multiple charges but couldn't say what those are pending approval by Crown prosecutors.