I have to be honest in that it is a LONG boat ride from Manuel Antonio to Cano Island, especially if the seas are even slightly rough. With that said, Oceans unlimited does the trip, Ninas Boat Rentals may be able to help you, or there are several fishing charter boats in our area that will take you for a wonderful snorkel day. Since gas is so expensive here, most people that really really want to do this trip drive to Dominical or Uvita and catch a tour company from there. Even from there you are looking at at least 2 hrs each way by boat, and around 45 mins drive to the Uvita area each way, so it can make for a long day with almost 6 hrs just in travel. Alternatively, there are local options with Planet Dolphin or Sunset Sails (or Ninas Boats) to just snorkel around Manuel Antonio. Granted, it is not as nice as Cano Island, but they are all enjoyable tours nonetheless. Enjoy!