Here's a baby polar bear, being raised by hand at a German zoo.
Recently, I've been kind of missing Howard, my old buddy, who is, no doubt, deep in hibernation in his swamp. I think I'd have a real problem raising someone like this, although I suppose it's easier when there isn't a release planned. The advantage with Howard was that he would never trust you or become affectionate, so you didn't bond in the same way you would with something that responds on this level.
That's really critical. With Howard, I was able to decide it was time to let him go because I only touched him once a week or so when I was cleaning his habitat, and, in those times, I was coming to the realization that he was getting too big to be safe to handle.
With the constant interactions involved in raising a polar bear, the moments of affection and danger would alternate and you'd probably wait to make the decision that you really needed to stop trying to handle her until after you had been mauled or killed.
Or at least, I would. Gotta admire the folks who do this sort of thing right.
Mind you, as I watched her being bottle-fed and was chuckling over the milk that ended up on her snout, it suddenly occurred to me that there's somebody I have to really admire -- that's the person whose job it is to take the bucket and stool into the mother's cage each morning and evening ...