OK, You are very tight on time, if you want to consider including Seward?? I strongly suggest you add a day. Although, change fees, it would offer you far more.
What time do you arrive in Anchorage??
Second point- you have some skewed ideas about Denali park. Frankly, read up on it prior to going, www.nps.gov/dena
It's all about access INTO the park, not what "commentary" there may be. It's about scenery, wildlife, not about some endless talking. IF you want to spend the day there, then you need to consider the shuttle buses. You then have the option to get off and walk around anywhere you wish. Biggest factor, is the cost. The "tour" buses are triple the cost. June 1 opens to Eielson, prior to that it would be Toklat.
Another problem, Seward is not a day trip and Prince William Sound is out of Whittier, not Seward. Seward is Kenai Fjords. PWS fits in perfectly your embarkment day of your cruise.
The ONLY suggestion I have with your current timeframe, is 2 nights in Denali park, a night in Talkeetna/Palmer/Anchorage/Girdwood. Early departure to Seward, Kenai Fjords boat tour, over night, then direct to Whittier. This makes the best use of your short time, and allows both Denali Park and Seward. BUT it involves a costly one way Anchorage/Whittier car rental with Avis. Pick this car up, as you go through Anchorage your last trip- not for the whole rental. You need to look at "costs" in other terms than money.
IF you happen to have an afternoon Anchorage arrival, then I would suggest you head to Seward by car. Overnight, next am- do the 8am Kenai fjords boat tour, and make your way back to Anchorage. Continue to Denali Park next two nights. Back to Anchorage. Then train to Whittier.