Drive to Asahikawa city and taste sake at Otokoyama sake factory. How about ramen lunch at ramen village? Then drive to Sounkyo onsen resort in Daisetsuzan national park. 2 waterfalls called “Ginga falls” and “Ryusei falls” are there. Autumn leaves must be beautiful in early Oct.
Overnight in Sounkyo

If mid to late Sep, we recommend to go to Mt. Asahidake where is the first autumn leaves in the season in Japan. Then drive to Biei town, and see Aoi ike-blue pond and Shirahige falls another famous autumn leaves spots. Just drive around this area is enough to feel autumn in Hokkaido. Stay in Shirogane onsen in Biei tonight.
Overnight in Shirogane(Biei)

Move to Furano area about 40 minutes drive. Tourist attractions are farm Tomita, cheese factory, jam garden etc. Autumn is the harvest season. Shopping and dining at Furano marche is good idea. It takes about 2.5 Hrs back to Sapporo.