vaneska - Welcome to cruise-chat- THE place to be when you want to do all things cruising! If you are on your way to the Panama Canal area on the Carnival Freedom -then by all means take the canal crossing tour-It is pricey(nearly $200) but well worth the experience!
As an alternative - you might consider a side trip to the old Galleon port of Portobello, sacked by the pirate fleet under Henry Morgan which will inlcude a visit to the Gatun Locks. Less expensive yet equally fascinating! I will be doing the same cruise in Jan 2011 on the same ship!