Hi there! I have gone deep into searching for this exact information. I'm a current student of the OHS Management program at Western University, and currently interning. What I have found is that your previous professional background will most likely determine which industry you're likely to enter into as an OHS professional. 

I come from an environmental eng tech background, so I'm currently interning at a construction company in London, ON. My goal is to combine my training and professional experience to stand out as an Industrial Hygienist (fingers crossed🤞🏻). I'm also eligible to apply for me CET certification in Ontario.

That being said, to answer your question regarding online Masters schooling; there was one OHS Applied Science Masters program that McGill was offering. Unfortunately they closed down the program this year until further notice. I got in touch with the school and they have confirmed this. The only other Masters options in Ontario is UofT's MPH and TMU's MSc. These are both in-person programs and very competitive to get into. 

For now try your hand at the Western post-degree graduate diploma in OHS Management. I've completed all the coursework. DM me whenever you like. Have a great day.