Frankly I would NOT pick anything that is more than an hour. That age is just too unpredictable not having a "way out". Excursions are costly- including a 3 hour train ride, and you can't guarantee no disruptions. I am not trying to be judgemental only factual. That age likes to run around and isn't always receptive to range limits. I would consider some port walking tours- especially in Ketchikan with plenty of things of interest- Creek St., totems. lumberjack show?? On the ship- I would try and arrange baby sitting right when you get on for some of the dining times- otherwise be prepared to leave possibily?? Again few toddlers can tolerate extended dining and multi courses. There was a good article in Cruise Travel Magazine giving excellent tips traveling with this age- the babysitting was a must.
I think it was the April issue? See if you can get a copy? Take a stroller it will allow naps and some mobility limitations in crowded ports.
Have a great trip.