Something I came up with while reading about polar bears and tigers. Since polar bears presumably evolved from grizzly-like species that moved northwards, what if tigers had filled their niche instead? So this isn't so much a hybrid as a speculative species (not that I'm an expert on evolutionary biology by any means!)

Some changes I made to the familiar tiger species: larger, muscular legs, long front legs and huge shoulders, shorter head for maximum bite force, short ears and tail to reduce heat loss, white coat with stripe pattern faded, something like a liger's markings but better camouflage than a white tiger.