Based on my experience, a work permit can only be issued in the immigration UPON ARRIVAL to the airport (if outside applicant). If you have an existing work permit HERE in Canada, then they will mail it to you, because there’s no such thing as a soft copy work permit, only a hard copy.
They will give you a letter to claim the work permit in canada airport. So you have to print that email to show it to the airport. Because airport departure usually look for a work permit AND work visa. A work visa is DIFFERENT from a work permit, does it makes sense? So you have to point them to that sentence “work permit will be issued upon arrival”. The airport personnel DOESNT know about that (in my experience, they had to call their boss because they don’t believe in the letter that I showed them)