Ahoy there, William! Thanks for sailing our way here at planDisney.
Ah, Alaska. One of the few remaining itineraries my wife and I have on our bucket list on Disney Cruise Line! We actually had one booked for this Summer, but that was before our son was born, and we figured he'd get more out of an Alaska itinerary when he's a bit older! We'd really love doing an active Port Adventure like you're hoping to plan for as a family, so I think we made the right call - even if it means we have to wait to say hello to the Disney Wonder just a bit longer.
I can only imagine how cool it will be to be that close to the Davidson Glacier! You got me interested so much to the point that I dove on into the frigid waters to check on how long the Glacier Point Wilderness Safari Port Adventure is offered. As of this writing, I was able to confirm that the availability of this Port Adventure will be subject to the port arrival schedule and also depends on which provider is selected by Disney Cruise Line to offer the Port Adventure.
Unfortunately, there's no way of knowing which guide company will be selected ahead of time, so my best advice would be to look for the Glacier Point Wilderness Safari in the list of Port Adventures for your day in Skagway once your booking window opens! If it's is there, and available, you'll be just a few months away from an incredible adventure! If it is not listed on that day, it's likely that there were no providers selected or available for that day.
Now, if you're open to other Port Adventures to have in your back pocket if your first choice isn't available, I've got three "planDrew-approved" suggestions based on my conversations with some friends who've stopped in Skagway:
Well, William, whatever you choose, I wish you and your crew a magical adventure in America's Final Frontier! Thank you so much for your question, and if you have any others as your planning continues, please drop me another line here at plan Disney!
Until then, fair winds and following seas!
Andrew