An open work permit is a work permit that is not job-specific. It allows your spouse or common-law partner to accept any job with any employer. If your spouse or partner gets an open work permit, it is normally valid for the same period as your study permits.
If you are an international student studying full-time and have a valid study permit, your spouse or common-law partner can apply for an open work permit. Your conjugal partner will not require a job offer to apply, and his/her permit will be valid for the same period as your study permit.
Your spouse/partner can apply for a work permit before or after they arrive in Canada. The work permit will usually be issued for the same length of time as your study permit. Your spouse/partner does not need a job offer to apply for a work permit.