bring spare battery as the battery drains faster in cold temp.
bring lots of memory cards, hokkaido has lots of nice scenery to take
if using centre weighted metering, over expose your exposure to get the snow back to white instead of 18% grey
I was in Hokkaido last December, and although no DSLR with me then, I think the conditions may not exactly be that bad for a DSLR. Just bring extra batts, and make sure you do daily maintenance with your camera. It can get wet quite easily when it starts to snow.
Also, don't be too overly protective about the camera. If it is a holiday right, just enjoy it. Precautions like take out only when necessary is pragmatic, but it depend on your preference.
For me i went to beijing a few years back even tho i didnt have a dslr then i had a camera..so yea..battery drain very fast to spare batt is a must and i put a heat pad with my camera...so my camera is always warm and toasty..idk if it'll work with a dslr tho...nv try