I have upgraded on these flights easily, the UG cleared way before the 4 day window. Now, this is the first time we are booking an S fare from NRT to YYZ, so I am curious as to where S sits in comparision to Q and L, probably lower on the food chain. All you have to hope for is that there are not too many SE's on your flight and not too many E's who have booked fares that are higher than S. Good Luck, it is a good flight.