Check out the pages for both ports at http://www.CaribbeanPortReviews.com
and you will find a ton of options. Your ship will probably do the Gatun locks (in and out) before visiting the Cristobal Pier in Colon, Panama. You should consider booking a shore excursion from the ship as you will not be able to get off the ship while it is in Lake Gatun. There is not much to see during the short stay in Colon.
Hope that helps.