Take National Route 231 out of Sapporo. You will cross over the Ishikari River (narrow bridge, better to take the walkway) and go through Ishikari. From the hilltop after Ishikari you have a nice view of Sapporo behind you. Until Atsuta you will have a few up-downs and then follow the coastline. After a few tunnels you will leave the coastline. An ascend takes you to a 2km long tunnel and then is a descend to Hamamasu. On the whole way there are a few convenient stores.
2. Hamamasu-Tobetsu-Sapporo (120 km)
In Hamamsu turn right and follow National Route 451 to Hamamasu Onsen and Takikawa. Very few traffic. No food and drink supply for the next 40 km. Flat until Hamamasu Onsen (3km) and then steady and easy slope for the next 15 km. Then medium ascend and steep descend. After a total of 24 km turn right to Tobetsu and follow Hokkaido Route 22. Hilly up-down along the valley and medium up-slope before the Aoyama Dam. Descend and afterwards fairly flat. After 20 km on the Route 22 you will meet Hokkaido Route 11. After 3.5 km you have the possibility to turn left to Tsukigata and then in Tsukigata turn right and follow National Route 275 to Sapporo. When you don't turn to Tsukigata but continue towards Tobetsu you will pass a quarry and from there the traffic with trucks on a fairly dirty and dusty road will increase. After 22 more kms you can turn left and take a bypass to National Route 275 just before Tobetsu. If you continue to Tobetsu you will meet National Route 337 and turn left to National Route 275 towards Sapporo.