A visitor record is a document that CBSA (Canada Border Services) will give you, or attach to your passport, that tells you when you must leave Canada. The duration of a VR varies and is solely at the discretion of the Border Officer that you encounter upon entry into Canada.
If you are issued a visitor record, you MUST notify CBSA when you depart Canada, to prevent any future problems. However, you can apply to extend your stay (usually done online), prior to the exit date on your VR and could legally remain in Canada until a decision has been made on your request.