Speaking strictly for the Alaska part....it's hard to make recommendations without a bit of narrowing it down: are activities (i.e. hiking, climbing, fishing, hunting ) preferred or observation? By mid-September in Alaska, the "tourist" attractions are beginning to shut down: many flight seeing operators, excursions, fuel/lodge infrastructure, etc.
I'd suggest some variant of a wildlife / scenic excursion out of Seward into the Kenai Fjords Nat. Park. I believe they run those through mid- if not the end of September, but I haven't taken one in a couple of years, so can't be sure. Unfortunately, in mid-September, both bear viewing and whale watching (if either are of interest) are pretty sketchy or non-existent....you can always see resident bears or resident Orcas / porpoise / seals / sea lions, but the big bear gatherings or the gray whale migrations are over.
Whittier (sort of on the way to Seward from Los Anchorage) offers glacier viewing tours through September. Focused on glaciers, so any wildlife is luck of the draw.
If McKinley / Denali sightseeing is of interest, I believe there are still options in Mid-September from both Anchorage and the Denali area....and seeing Denali on a clear fall day is pretty spectacular.
If you have an interest in fishing, while weather conditions get generically dicey in September, there are lots of options for saltwater (silver salmon, halibut...although tailing off, possibly rockfish, etc) and freshwater (Silvers, trout) fishing. Freshwater would be from Anchorage or the nearby Mat-Su area (Willow, Wasilla) or Kenai Peninsula (Soldotna, Kenai), while saltwater would be very do-able from Seward.
Just for road sightseeing, even as a dyed-in-the-wool "there's nowhere like Alaska" guy, the trip on the highway past / through Kluane is incredibly spectacular. In Alaska, presuming clear days, the stretch between circa Trapper Creek to Nenana (on the Parks Highway) is incredibly scenic. Similarly, the Seward Highway from Los Anchorage to Hope can be very scenic. Not on your list, but the Richardson from Glennallen to Valdez is arguably one of the most scenic drives in AK and the stretch (on the Glenn) between Palmer and Eureka is also quite scenic. Lastly, in mid-September you'll be fighting the hunters (legit and lazy road hunters) but the Denali Highway (between Cantwell on the Parks and Paxson on the Richardson) is my favorite drive in Alaska.
CRL
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