I get what you are asking, and think he'd be cutting it to close. With that positioning flight being on another ticket he is one delay away from risking the whole MR - there is no guarantee that the same AC operates the return route to ORD (the start of his MR). I'd get to YYZ a little earlier just to be safe.
Also, there is lots of YYZ transit information here:
http://www.flyertalk.com/forum/canada-462/