If a work permit has not expired yet:
According to Canada Immigration rules, a foreign worker (FW) can apply to extend a work permit from within Canada if the work permit is still valid. FW can extend a work permit for a period of time that adds up to but does not exceed the maximum of four years of work in Canada.
FW may get an extension if
- FW applies for his new work permit before his current work permit expires;
- FW and the employer sign a new employer-employee contract, if applicable; and obtain a new positive LMIA,
- The employer pays the employer compliance fee and submits a new offer of employment through the Employer Portal if the job does not require an LMIA.
To apply to extend a work permit from inside Canada, FW must apply online; or send an Application to Change Conditions or Extend Your Stay in Canada as a Worker to the Case Processing Centre in Vegreville, Alberta.
FW must submit an application before the current permit expires. FW will then be allowed to stay in Canada until a decision is made, and FW may continue to work under the same conditions and FW will keep the current status until a decision is made.
If a work permit has already expired:
FW can apply to restore the temporary resident status and extend the work permit from within Canada. FW can only do within 90 days of work permit expired, and cannot work while this application is in progress. The fees for both the restoration of temporary resident status and a new work permit must be paid
 Visit online http://www.cic.gc.ca/english/work/apply-who-permit