Why not?
YYZ-CUN
pgrade to Business Class:
Fare NameBooking classNumber of eUpgrade Credits required to upgrade to Business Class (per passenger) Upgrade request
Premium Economy (O)2 Anytime
Premium Economy (E, N)10 Within 14 days
Latitude (B, Y)2 Anytime
Flex (H, M, U)5 Within 14 days
Flex (Q, V)10 Within 14 days
Tango (A, F, G, K, L, S, T, W)15 Within 1 day
Who cares where he bought the ticket, if it has an AC PNR, its booked into one of those fare classes why would the system refuse it?