If you want to keep studying, you need to extend your study permit. If your study permit expires and you want to stay in Canada and study, you’ll need to apply:

• for a new study permit, and 
• to restore your status as a temporary resident

When to apply? 

Apply for a study permit extension at least 30 days before your study permit expires, if you want to keep studying in Canada.

If your study permit expires and you haven’t applied for an extension, you need to restore your status to continue studying in Canada. You must apply to “restore your status” within 90 days of losing it, meaning you have a 90-day window to re-establish your legal right to study in Canada. 

If you apply before your permit expires, you can continue to study under the same conditions as your current study permit until a final decision is made. This only applies as long as you stay in Canada.

If you apply after your permit expires, you can stay in Canada but may not continue to study until your status has been restored and you have received your new study permit.

If you finish your studies earlier than expected, your study permit will expire on whichever date comes first:

• the date marked on the permit or
• 90 days after the day you complete your studies

If your spouse, common-law partner or dependent children came with you to Canada, they may also need to restore their status.

Extension and Restoration Requirements

• Proof of acceptance at a Designated Learning Institution
• Provincial attestation letter (PAL) or territorial attestation letter (TAL) if applicable 
• Custodian Declaration if applicable 
• Proof of financial support while you study in Canada
• Are in good health and pass medical examinations if required 
• Give your fingerprints and photo (biometrics), if required 
• Must meet the requirements for temporary residents 
• May require some other documents depending on your situation 

[Source] https://www.canada.ca/en/services/immigration-citizenship.html