My husband visited me often while I was here and we were waiting. I believe he re-entered Canada a total of 7 or 8 times during the process, every time on visitor status and he did not have a problem. He would tell the customs agents that we were in process for PR and that he was visiting me and they seemed to be alright with that. He only got a hard time once but it wasn't anything major.
He did also maintain work in the UK so perhaps that helped? But if they can see that you are going through the right channels to get PR then I think it should be alright.. correct me if im wrong, anyone else?