I got confused, your has an OWP right now, or he is a temporary foreign worker?
If he has an OWP right now, and you applied for OWP with your sponsorship application, than he can continue to work while your application is in process, so he shouldn't change his status to visitor.
If he is a foreign worker, than (AFAIK, pls correct me, if I'm wrong) he won't be able to work after his permit expire. But he will get implied status with the OWP you sent, so he will have legal status in Canada. In this case you don't need to change his status to visitor, but it won't hurt either.