Same issue last year
I booked a trip last year through ACV. I have had tickets booked through my work and I was always able to upgrade to a T+ class for a few bucks. NOT with ACV.
ACV cannot upgrade you to a T+ class. I called repeatedly.
AC was unable to as ACV simply block books seats. AC could not help me.
They are 2 entirely different companies.
In the end, I cancelled my YYJ-YYZ portion (in G class) kept my YYZ to cuba portion (J seats, 100% aeroplan miles) and simply booked a new ticket YYJ to YYZ from AC.
I would cancel and only use ACV for the portion of your trip that is outside Canada booked into executive class