Ontario Provincial Police (OPP) say the driver of a garbage truck might have forks or a lift bin in the front, and could have been elevated at the time of the incident.
The damage included a large section of the ceiling panel that crashed down onto the roadway. Thankfully, no one was hurt.
Detours are in place as the tunnel is closed until tomorrow, potentially longer.
OPP say investigators are speaking to the driver for more information.
Diana Weeks with the latest.