Hey I was wondering I am planning to go to Toronto but my visitor's visa has expired, it is in the process of being extended but I wanted to know if I would need a valid one to travel within Canada.
Yes, but airlines can choose not to board you if you don't have one, and it is within their rights to do so.
IF you read the news, there are alot of cases like these. Someone is legally allowed to enter canada by plane or by land, but can be stopped from boarding the vessel because of missing TRV. No one can do anything about it because it is already written and acknowledged by you on the contract of carriage.