@amanda5: Yes, I would assume that you would lose your $500 deposit if you accept an offer to Lakehead and then decide to go to another school. Also on the Lakehead admission letter, it states that you can accept only one offer at an Ontario university and to let graduate studies know if you decide to accept admission to another university. Sounds like they know their March 20 deadline is earlier than other schools and they are profiting from the waiting game.
After some thought, I decided to accept the offer from Lakehead as this program is one of my top ranked programs and I really doubt that I would hear back from the other programs that I applied to by March 20 (going by past discussion threads) . I got a response back from Grad Studies confirming my admission response and deposit and that they will let me know when registration is starting for the MPH program in September.
After hearing from a few that Waterloo is already letting some know of application rejections, I checked my application status and am continuing to wait to hear back from the department for both the MPH and health informatics programs. I am also waiting to hear back from MUN as well for the on campus offering of MPH program.