"Cajun" music often has accordions, maybe harmonica and fiddles, but it's more about the FEEL than the instrumentation. Hard to explain. I'm in Cajun country and do a lot of the songs, but it's not the same as a real Cajun band.
Also, there are many variations of Cajun music, just as there are Jazz, or Rock or Country.
Still, if you hear a song by an authentic Cajun band, you KNOW what it is.
This doesn't help does it.