OK, what information I can scare up on the size of Arctodus simus states that it's a bit over 5 feet tall at the shoulder on all fours, and when upright is 11 feet tall or more. It also says it weighs 1,800 pounds. Can't find anything about its length on all fours right now, but based on the pictures I can find I guess it's about 8 feet long from nose to bum.
Cold and temperate plains for environment?
Here's the flavor text I've come up with:
This immense, long-legged bear has a face like that of a mastiff. It rears up on its hind legs, standing as tall as a fire giant, and lets out a mighty roar.
Among the bears, the giant short-faced bear is second only to the dire bear in sheer size and ferocity. Other animals know to stay out of the way of one of these beasts - its roar alone is usually enough to drive smaller carnivores from their kills, and anything that refuses to heed its warning faces its deadly claws and teeth.
Combat
Before entering combat proper, a giant short-faced bear attempts to scare off any smaller creatures with its roar. A giant short-faced bear attacks by tearing at opponents with its claws.