Keep your old passport. If you plan to travel outside Canada, bring both your old and new passport with you. You’ll need your valid work permit when you come back.
The expiry date on your work permit is linked to the expiry on your passport. If you got a new passport because your old one was expiring, then your work permit will also expire at the same time. In this case, you need to apply to extend your work permit to keep working in Canada.