Which Breed is this Cat?

He's between 6 - 8 months old, came by himself to our house most probably lost his tracks to go back home or someone dumped him nearby and he followed one of the neighboring cats who come daily for food but didn't go out.

We are trying to figure out his breed, the vet was not certain whether it's a Persian mix or British long hair, features like very wide and thick legs look more like Siberian, if someone's an expert, do weigh in please.