Personally I wouldn't bother with the polar bear but I'm sure there are others who would love it. I suppose it would be possible that a few from zoos may survive and breed. The dogs are a great idea for wandering animals though.
Seconded. Polarbears - why!?
I could completely understand mountain lions (in NA), Lynx (NA/Eu), black/brown bears (NA/Scandinavia/Russia and so on), but not a polar beer... even if the ice froze there would hardly be prey for it all the way to Europe!
But, really, I mean what's next - penguins?

(Yeah I know Far Side messed that up - North Pole/South Pole)