It sounds feasible. You can do a lot in Seward in a day, including the Sealife Center (it isn't that big). If you go out on a boat to do a Kenai Fjords tour, that can take up most of the day, though.
Portage Glacier and the Alaska Wildflife Conservation Center are both along the Seward Highway near Girdwood and could be fit in as well.
A lot of the touristy stuff in Anchorage is in downtown. Some other things are the Alaska Zoo, Earthquake Park, the coastal trail, and Kincaid Park.