Any good suggestion for Hoikaido?

otaru(小墫) is also good for sushi, and sightseeing, and buy glass products.

and you can also go to shiroi koibito factory, which is sort of on the way to otaru from sapporo.

don't forget about dairy and cattle farms, lots of good japanese cow products in hokkaido.

and i second the idea of going to noboribetsu for hot springs.  it's good any time of year.