on the Camry i have 2" pipe catback no muffler, resonator through to cannon, it is loud enough for my liking, and sound awesome on higher revs.
2" would do you fine from cat back, but 2.25 you could do, but as you get into higher revs you might get this fart/tiny noise that sounds like shit, and you will loose power from it, i would go with the 2" with tuned length custom extractors.