Itasca is a great park, but it is about an hours drive from Walker. If you are coming from Minneapolis, I have a couple of recommendations.
1) stop in at Mille Lac Kathio state park. You could do a hike there and see the colors.
2) drive around Gull Lake just outside Brainerd to see the colors. Stop in Nisswa for lunch or shopping.
3) You can do a hike right outside Chase on the Lake. We've been there in the winter and have snowmobiled on the trails. I'm guessing at this time of the year they would be beautiful.
Whatever you do have a wonderful time. Chase on the Lake is a great place. Make sure to eat dinner in the restaurant for a beautiful view of Leech Lake.