It depends on the work permit you have. Most work permits are tied to a specific employer. They will only allow you to work for the employer on the permit.
In some situations, you can get an open work permit, which does not include a specific employer. An open work permit allows you to work for any employer in Canada unless the employer:
is listed as ineligible on the list of employers who failed to comply with the conditions, or
offers, on a regular basis, striptease, erotic dance, escort services or erotic massages.