jerry-congrats on your cruise.
first of all know one will ever know what side of the ship you might sight a whale. they will be around but are very unpredictable. sightings from the ship do happen but they dont happen that often and it is over in a matter of seconds. so for each of your ports here are some suggestions=========
juneau--a whale watching tour in my opinion is a must. either with the ship or an independent co. capt larry is the best but he books very early
www.orcaenterprises.com the tram is right by the ships where they dock. also in juneau is the mendanhall glacier. right on the dock are blue buses that will take you there for $10 roundtrip. get on and off at will. helicoptor rides too the glaciers are famous here as well. there also is the brewery==www.alaskanbrewerycompany.com. ( i hope that is the right address). i think the tour is free.
ketchikan is popular for floatplane trips to the fjords. also that is where the totom poles are --saxman village and totom bite park. kayaking and fishing is popular also along with just going a few blocks from the ship and walking on creek street. interesting spot and good shopping. bear tours are popular here too.
skagway--the white pass railway train ride. you can get a pass at skagway or get a tour on the ship for the trip. gold panning, horseback riding, dogsledding and van trips into the summit are popular here as well as helicoptor rides here too.
of course each port has very easy trails to walk, the salmon will be on the run so eagles will be everywhere as well as bears if you are lucky enough too see one and shopping, shopping, shopping..
there are hundreds of posts here that will have lots of info on all of your ports and how to have the best time for the money while you are visiting them. have a wonderful time and go surfing the net for each port. you will be able to link onto many sites to let you know much more. and i know other members here will be helping you as well. i hope this helps. have fun