We were on the train from Fairbanks to Denali. There really isn't much opportunity to see any wildlife on this part of the trip. You are traveling through the interior and you will just primarily be seeing trees on both sides.
We were on the train also from Denali to McKinley Wilderness Lodge. We were on a coach from McKinley down to Kenai. It never slowed down for viewing anything and it's all a very long ride.
Personally, we decided that we would rent a vehicle and do the driving ourselves if we have the opportunity to go back. We loved Alaska! The best viewing is from boats, ships and from the air. I would recommend budgeting the most for those activities to really see Alaska. And if you want to see wildlife, plan your excursions for the early morning or early evening. That's the best time.