According to Const. Jean-Pierre Brabant of Montreal police, two masked and armed suspects walked into the bank around 10:30 p.m. ET Thursday before the Garda truck arrived.
The thieves allegedly tied up a janitor while they waited, and then tied up the two armoured truck guards when they got there.
Police believe they fled in a different car than the one they drove to the bank in.
It is unknown how much money was stolen.
There were several armoured truck robberies in Montreal and on the South Shore in 2014.
The union representing armoured truck guards has been calling for a third guard on duty for years.