I assume you are talking about interior Alaska cruisetouring??
If you are starting in Fairbanks, I STRONGLY suggest you plan on coming in at least a day early, 2 is better. Most cruisetours otherwise see very little of Fairbanks, take advantage of being there- a car rental is necessary.
Be sure to book a tour with 2 nights at Denali park and the Tundra Wilderness tour- but do realize, this really isn't the best option into the park. My min. distance in is Eielson, 10 miles further, and ideally Wonder Lake. These are both gotten to via shuttle bus.
Look for a tour, that has an overnight in Seward- or if you have the last night in Anchorage, ditch the transportation to Seward and purchase the Alaska RR yourself and get into Seward in time to take a Kenai Fjords boat tour- a must do and highlight of Alaska travel.
If you are open to it, it is very simple to also just go on your own for usually significant savings and the ability to pick up the best of Alaska.