If you’re an International Experience Canada participant, see Extend or change your work permit – International Experience Canada.
You can apply to restore your work permit in the first 90 days after it expires. If you do this, you can stay in Canada until you get further instructions, but you must stop working until you receive your restored work permit. There is no guarantee that your application will be approved.
Otherwise, you must leave Canada right away when your work permit expires. If you do not leave, you could be deported and will need permission from an immigration officer to come back.
Find out how to restore your work permit.