THE SHORT ANSWER
A visitor visa is a travel document; a visitor record sets out an authorized stay in Canada. A visitor record does not authorize re-entry.
Which document do I need?
Start with your goal: entering Canada, extending a stay, or travelling while studying or working. These are different questions. Your passport, citizenship, current status and travel plans determine which requirements to check.
Does extending my permit renew my visa?
No. IRCC does not automatically issue a new visitor visa when you extend a study or work permit. If you need a new visa, a separate application is required.
What should I check before travel?
Review the expiry dates on your passport, visa and permit separately. A document authorizing your stay is not a guarantee of entry. Check the official travel requirements before making arrangements.
Go straight to the source.
Confirm the current instructions with IRCC before applying. These links are official Government of Canada resources.