For AC, I'm not sure where Op-Ups are in the listing, but it differs from other airlines. AC will not Op-Up a person just to fill the cabin - they'd rather fly with an empty J seat than fill it randomly with someone who isn't spending credits on an eUpgrade.

Op-Ups can happen for a variety if items: discretion of AC, due to weigh-imbalance (happened twice to me), mechanical/oversell issues, etc.

But AC will not simply upgrade a status passenger to J if they didn't request it, to fill a cabin. I've been on flights where J was at 40% cpacity - and this was a pod-flight between YYC and PVG!