Just Some Random Thoughts
As long as you're leaving from Seattle, taking the land-based roads north, and have a bit of time for the journey, you might want to consider heading a bit farther inland than you might otherwise and visit Jasper National Park. Including this 'little' side trip would only add about 250 miles to your overall drive and would be well worth it.
As for the return trip, I'm going to suggest that you spend more time on the boat. If you head all the way up to Fairbanks on your outbound leg (recommended) then come down through Denali and Talketna to Anchorage and Seward (also all recommended), then driving all the way back to Haines to catch the ferry home doesn't make a lot of sense. I think you'd be far better off leaving from Whittier, with a stop-off in Juneau (only reachable by ferry) and then continuing on to Port Hardy at the northern end of Vancouver Island. Then you'd just need a final ferry ride from the southern end of the island to either Tsawwassen BC or Port Angeles WA to complete your journey.
Such a return journey would maximize the number of new sights you get to see including the chance to drive through a railway tunnel (the only way to get to Whittier). see the Mendenhall Glacier, and drive the entire length of Vancouver Island. Anyway, as I said, just some random thoughts.
AZBuck