In the post AC/CP merger there was a mix of 763's with 25 and 30 seats in the fleet. At that time AC would only sell 25 J seats even if the scheduled aircraft was going to be a 30-seat version. The 5 extra seats, when available would be used for people with upgrade certificates.
Maybe AC needs to go back to that philosophy with the A330 and only sell 27J and 21 PE until such time as all the aircraft are upgraded to tht new layout. That will make people using eUpgrades happier as there will be better odds of scoring an upgrade.