Thanks so much for your detailed answer. It was really difficult, particularly the cruise line material didn't explicit say which locks the ship would be using either.
I am happy to take my chance now that I know it fits the Panamax size and accept the risk that some unforseen circumstances could change it to use the new locks. It's actually surprisingly difficult to find the right Panama canal full transit cruise with the right itinerary and dates!
I did research on Wikipedia, and I saw:
32.20 m (105 ft 8 in) (hull)
35.64 m (116 ft 11 in) (maximum)
And I was not sure which measurement is the most important one. The hull beam seems to be just under, but not the "maximum".