I live in Alaska but actually haven’t done much packrafting since moving.
Based on other reports the Brooks Range is an obvious choice for your goals. There is good rafting in other areas but if you want small volume water you’d want to wait till fall. But don’t go to late. A friend of mine biked into a non motorized area and shot a moose 3rd week of September. An early storm dumped a foot of snow and they had to hike out, get skis and pull the meat 20 miles on skis (made me glad I didn’t go along!).
In fall the Wrangle Mountains should have lower water, greay colors and you could see some glaciers.
The Kenai Pennisula is nice but longer trips would be harder to put together.
The Alaska Range has some good options but will be a bit busier in hunting season (August for Caribou, September for moose). Might be hard to hire a bush plane.
You might do a shorter trip in Denali just for the experience and wildlife viewing then another longer trip somewhere else.