I have taken this trip twice. The 2nd time we booked a balcony room and loved it. Pictures were taken were a Sigma 28-300 and turned out beautiful
In Vancouver take a side trip to China Town, Queen Elizabeth gardens, And Stanley Park
On embarkation if from Vancouver take a pic as you pass the bridge in Stanley park heading out to sea as well as the sunsets
In Anchorage take in Mendenhall Glacier and a whale watch your. Did not regret it
In Ketchikan Totem Pole Village was interesting
In Skagway the train trip afforded many photo opportunities
The trip through the glacier area and watching the calving process afforded many shots
The train ride ide is excellent but take the shots at the end of the car you are in.... better shots. Some good chances for getting the train rounding a few bends also Poor shots in the domed cars The best memories I have are the shots when leaving Denali .... need to be ready for about the first 1/2 hour? or you may miss some good ones. Some good chances also on the school bus in Denali.... hope for clear days to shoot the mountain.
I only used the single lens and did not regret taking others.
I hope this gives you some things to think about as it it a trip of a lifetime
First and foremost.... enjoy yourself

Photographers sure are different, aren't they? Took the trip a couple years back. Big country for me equals wide angle lens for the "Grand Scenic" shots and long teles for the wildlife (although the bears I saw were less than 100 feet away). Where Billnikon "never takes a tripod", I always take and use a tripod. If the auroras are out, you'll probably wish you did, too. Yes, I'd recommend taking the 28-300mm. Lot of shots from that one lens. On the boat, I mostly hung-out at the bow for glacier shots, but you've got legs. Use them. The boat ain't all THAT big. Mostly enjoy yourself. Remember, Alaskan weather "ain't no picnic." Unless you are Blacks2, you'll see less sun than clouds.