It isn't possible to be sure, but the French derivation is usually considered most likely. You'll also find people suggesting that it derives from shanty (as in a cabin or hut; derived either from French chantier or Gaelic sean tig; again, even serious lexicographers cannot be certain), but that seems a bit contrived, and I've never seen a convincing argument in its favour.

The question has been discussed quite a lot here in the past, I think: probably in the main in the course of other discussions, so although the onsite search engine will find those references for you if you ask it the right questions, you'll have a fair bit of weeding to do along the way. You won't get an easy or definitive answer (there isn't one), but you'll learn interesting things so long as you keep in mind that most of what people say on subjects like this is opinion (or, sometimes, fantasy), not fact.