My first guess just based on the color and shine of the dog is that it is either the phone booth or a postal box in the UK Pavillon.
Okay, so then I am on the right track that it is a postal box? Now it's a matter of where the box is. I'm going to move to another park with my next guess. But please tell me if I was in the correct park to begin with...Alas, your thoughts are very keen, yet my dog is not from the UK, but he does spend time chasing mail carriers.
Okay... So we rule out DHS and Epcot. And since you said temporary, my guess is that it is a Christmas decoration. So now it's just figure if it's at DAK or MK, with the more obvious choice being MK. Is there a temporary Christmas Card Mailbox at either Town Hall/Guest Services or by Santa Goofy (courtyard next to Guest Services)?