We're on the RCI Serenade of the Seas in August. The ship's itinerary has a line item for "Misty Fjords", but in fact the time is only two hours. It's a drive-by. If you look at a map, what the ship does is pass by the very southwest edge of the national monument on the way back to Vancouver. In essence, if you want to see the monument at all, you won't see it from this cruise ship.
Assuming all the cruise lines are similar, the RCI shore excursion for the flight to Misty Fjords is in a DeHavilland Twin Otter, essentially a commuter plane on floats. It carries a relatively large number of people.
I did some checking on private operators. Go into Google and input "Misty Fjords Flightseeing" and you'll get a whole bunch of them. Most of them have websites where they go into the services they offer in detail. They all do similar things, and they all charge pretty much the same, which is about $200 per person.
The advantage of using your private operator vs. the cruise line's own private operator is that the former use smaller airplanes, the excursions costs less, and they stay longer when they put down on one of the isolated alpine lakes in the monument.
We booked a tour today, and there will be just four of us on a DeHavilland Beaver, a floatplane well-suited for this kind of flying.
I also found out that their August dates are filling up fast, so it is probably a good thing to act on it quickly if you have a summertime cruise coming up.
Platinum for Princess, for Royal Caribbean and for Celebrity.