When you choose a starter they have their normal ability (Torrent for Froakie).
But if you really want a Protean Froakie you must get it from either a trade or Friend Safari. You can go to Friend Safari after you beat the Elite 4. You must have a friend with Water Safari with Frogiader (Froakies middle evo). You could also try GTS. Or try Wonder Trade for the luck of getting it.