I want to take a course in the health science program but it says it's only offer to BHSc III students. Who should I contact regarding this? Academic advising, health science office or the prof who teaches the course... please help!!!

Any of them. And if you try one and they can't help you, they'll just direct you to the person who can.
For example, you'd need the prof's permission, but if they grant it they'd probably direct you to someone who can actually allow you to register in the course.

I don't think you should get your hopes up though. It can't hurt to try, but if it's restricted then there is likely a reason and health sci-only courses are generally quite specific.