I am sitting here in the lounge in YYZ waiting for my 1745 flight to YVR. The lounge (domestic) probably has about 5 people . Some days they are full and some days they are not. At check in, I found out there are still 15 seats in J, i even got a single seat in J for this flight. I'm sure they'll find a way to fill all those J seats before takeoff.

A couple flight during the day in the afternoon are fully booked in J, sometimes it is close to empty, also found out that the 23:50 flight YYZ - YVR flight tonight has only 1 person booked in J class. So, if anyone is really looking for upgrade, book that flight, but wouldn't get into YVR til 3am. Better than getting 1/2 mile, right?

So, I think we cannot judge whether a flight is full based on its history, maybe in Y class, but definitely not J class with a couple of flight exception. (CP 7, CP 987) If you want upgrades, NEVER book on those 2 flight, you'll regret it later. And NEVER book on morning flight from YVR-YYZ.