First, the best way to preserve a hide is to salt it right away. Make sure to remove any chunks of meat and fat still on the hide. When you salt a hide you don't need to freeze it. It will keep for up to two years salted. NOTE - You do have to watch for mice and moth type infestations.
Unfortunately, if a hide is frozen for more than a year it doesn't turn out very well. The leather gets freezer burned which chemically alters the leather fibers. The hide will look fine after its tanned for a little while then al the hair will fall out.
Tanning a bear hide has a few extra steps. You need to turn the ears inside out,split the lips, and filet open the paws to remove the bone. Also, bears are very greasy (because of their diet) so you need to vigorously degrease the hide before you begin the tanning process.
Brain tanning is an interesting process. If you would like to brain tan the hide there are many resources out there. We don't currently offer any brain tanning advice.