Hi there!

I was in Japan last year, but it was in November. I'm guessing that the major attractions would be open all year round?
So sorry to hear that JR Tower is full, we had a great stay when we stayed there.

Are you interested in trips out of Sapporo? I had a day trip in Sapporo, and another in Otaru (a train ride away, it was pretty accessible). For Sapporo, how about Okurayama Ski Jump Hill and Shiroi Koibito Park? Personally, Shiroi Koibito Park is a must-see!

Don't wanna flood your thread here, check out my experience for Sapporo and Otaru. Hope it helps

I like to check out what tours are being offered and then "steal" their itinerary for our own use, so that's one more resource there for you.

Enjoy your Japan trip! ^