The plane, which departed from Edmonton at 7 a.m. M.T., was surrounded by fire trucks at Thunder Bay airport but there was no sign of flames or smoke.
According to a statement from Westjet, at about 9:30 a.m. MT the captain reported possible smoke in the cabin and decided to divert to Thunder Bay.
Two passengers also told CBC News there was an odour of smoke around the washroom at the rear of the aircraft.
There were 95 passengers on board plus six crew members, Passengers were taken inside the terminal after leaving the Boeing 737.
Westjet said maintenance crews are now examining the aircraft.
CBC News will update when more information becomes available.