Anywhere Lafayette (wife's family owns a famous Cajun restaurant there) or further South is fine as you'll essentially be in Cajun Country. If they sell cracklings or Boudin by the side of the road instead of snowcone stands, you're in the right place.

Lafayette, Baton Rouge, New Orleans are all great. The middle of the state (Alexandria region called Cenla for Central Louisiana) is a mixture of south Louisiana influence and the more Northern influences, so the Cajun influences are there, but watered down. Northern Louisiana is nothing like the rest of the state. With the exception of Shreveport and Monroe (maybe Ruston) it is mostly small towns and has a very Bible belt feel to it. Some call it "South Arkansas" as it has more in common with that region.

I've had gumbo and jambalaya made by Cajun family and the best places in the South and it's much better than anywhere else in the US when it is made properly. I've had plenty of what's called gumbo/jambalaya in other southern states and it is good, but doesn't quite taste right.