I did the tour while cruising on the Legend. Our ship was at port at Colon, Panama. We did not do the canal transit that I have done before on another ship. I suggest that you contact Celebrity, and ask for a copy of the tours to be faxed or emailed to you. This way, you will be able to find out what your ship offers. Our train trip was round trip to Colon. If your ship is transiting the canal, that takes about 6 to 7 hours, so I can't imagine you would be able to have a return train trip.
Bon Voyage