I watched some South Park episodes, and why I loved that series, Eric Cartman and Kenny McCormick are both almost identical to James and Oliver.
I remember Oliver the Great Western Engine, he is Western, just like Kenny McCormick. And what can say about James and Eric Cartman......at least for me they have very similar personalities,but the important point is that they both are vain, dumb, splendid and conceited.
Then about the rest of the gang,the election was very clear. Stan was the leader (so Thomas matches it perfectly). Kyle is innocent (so Duck has the perfect match), and Butters is the pussy guy) (so is Percy).