The expiry date on your Visitor Visa (also called a Temporary Resident Visa or TRV) indicates the last possible date you may seek admission into Canada. This date is on the counterfoil (or stamped) document in your passport. This identifies the person as someone who may be able to enter as a temporary resident if deemed admissible. Your visitor visa is no longer valid if you seek entry to Canada after that date. When you arrive in the country, Canada Border Services Agency (CBSA) confirms whether you are eligible to enter, and they typically set a 6-month period as the duration of stay depending on the type of application you present. In those circumstances, you would have 6 months from the date of entry. If you wish to extend your visa, you should apply at least 30 days before the end of that 6-month period. IRCC outlines all the rules regarding Visitor Visas. [See IRCC: Temporary Residents - Visitors]