We stayed at Takinoya in Noboribetsu for a night and the food was very impressive. We didn't do much in Sapporo/Otaru in terms of fine dining, given the cold temperatures we were more focused on soup curry and hearty fare.

You can see here the best of the 2017 Michelin Guide restaurants. I'm not sure which are still open/highly regarded but the Michelin website itself doesn't have the listings anymore.