My 18 year old's best friend did Alaska LAST year...and told our daughter that her parents MADE her take the train and it was the "most boring day of her life"...at least that's what she told OUR daughter...So, going in, with our daughter's protestations, we knew the train thing was a "no-go"...at least for the kids...
We considered taking the train ourselves and sending the daughters horseback riding (my older daughter's first choice excursion EVERYWHERE)...and finally decided to ALL do the horseback thing as a family...in some ways I am happy with that decision (with only six totlal on the trip it was very personal and special), in some ways I regret it (we were SORE from two hours on the horses!!)
At a minimum, send the kids on the horses...After 9 (out of 12) cruises with my kids, I think I've got a handle on what kids want...My guess is that if we'd done the train, both daughters would have slept through most of it (because they were up late every night on the ship)...