You have to find an employer willing to apply for a LMO by Dec 20th. If they apply for the LMO, you can apply for a new work permit(without the LMO) 2 weeks before the old permit expires and submit proof of the LMO application(e.g. confirmation # from HRDSC, etc).
You can then remain in Canada until CIC makes a decision on your application but you can not work until you received the new permit.
On the otherhand, if you are unable to find an employer, you can apply to change conditions of your stay to visitor(not permitted to work) before your permit expires. Again you can stay in Canada until a decision is made.
Note that if your work permit expires and you have not applied for extension or to change status to visitior, or your application is rejected, you have 90 days either from date of work permit expiration or from date of CIC's decision respectively to apply for restoration of your status.
