Lavigne, 39, joined Sum 41's Whibley, 44, on stage at the MGM Grand ... Whibley tied the knot with current wife Ariana Cooper ...

Previously, Sum 41 canceled their performance at Brisbane ... pneumonia and with the possibility of heart failure, which his wife, model Ariana Cooper Whibley, revealed in an Instagram post ...

The singer was joined by wife Luisana Lopilato, who sparkled in an asymmetrical sequinned pink gown with thigh-high cut out. Sum 41 hit the red carpet for the final Juno Awards performance as a band.

Weeks before, Sum 41 wrapped up the Tour of the Setting Sum ... ballad featuring Whibley on piano — then Whibley’s wife, Ariana, excitedly tells Cone they love “that little fuckin ...