To extend your stay in Canada as a visitor (stay in Canada longer), you need to apply before your current status expires. In case if the application is approved, you will be issued a document called Visitor Record, which is a document that says how long you can stay in Canada and includes an expiry date.
Note that this record does not guarantee you entry to Canada in case if you decided to leave the country during the extended stay.
The application for a Visitor Record is normally done online, but in cases of disability or encountering a problem while applying online, a paper-based application can be submitted.
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