If you are a visitor in Canada and would like to stay longer you can submit an extension request. Applications for extensions must be submitted before the expiration of your current status.
Once an extension application has been submitted you are given what is called "deemed status". This means that you are permitted to remain in Canada until your application request has been processed. If your request is denied then you must leave Canada.
Application extensions usually permit stay for up to an additional 6 months. First requests are normally accepted if all information requested is correct but additional extensions requests can prove to be more difficult to obtain.