Cartegena hasn't been on Princess's itinerary for a few years cuz of the drug wars so you may not get up-to-date info on that port.
As to the Panama Canal, I can't say enough about the ferry boat trip from Gatun Lake through the other 2 locks - really outstanding and gives you a whole new perspective of the locks from a small boat. Having said that I don't know what your whole itinerary is. I took the Island Princess when it first started out and they did the FLL round trip (as the Coral Princess does). If you're coming from the west coast, then forget that particular one.
Which ever way you're coming DO NOT take the train ride - complete waste of money ... most of the time on buses and speeds through Panama so fast that you can't take pix.
Have heard raves from the people who have taken the aerial tram but have not experienced first hand.