What is ～そう ? Is is the contrary of ～そうにない ? So it would mean something like : "It's likely that you will succeed if you do it the hard way" ?
"～そう" means "it seems", and "～そうにない" is the negative form. More literally, your sentence would be "Doesn't it seem likely that you will succeed if you do it the hard way?", with "じゃない?" meaning "doesn't/isn't it?" here.