I'm not an expert on this. But the following points are noteworthy:
According to CIC, "The HRSDC confirmation is typically given for a specific period of time, and the work permit will be issued
to coincide with this period. A work permit beyond the specified period will therefore likely
require a new opinion from HRSDC."
Also consider:
"Effective April 27, 2009, all employers participating in the Pilot Project for Occupations Requiring Lower-Levels of Formal Education (NOC C and D), Exotic Dancer, and high-skilled Program streams will be required to submit a new Labour Market Opinion (LMO) application. The application to extend a LMO will be removed from circulation and all references to LMO extensions will be removed from communications and outreach materials."
"In cases where employers anticipate that their human resource needs will continue beyond the period covered the temporary foreign worker’s work permit, employers are requested to apply for a new LMO four months prior to the expiry to ensure that ample time exists for the processing of the new LMO and, if authorized, the subsequent work permit request."