I interned at XJ (Mesaba) and I think the requirements were commercial and maybe instrument. Makes sense because I did do work that required knowledge from my training for both. Also went through crj-900 ground school. Someone without a commercial/instrument might have been able to do most of the job, as a lot was collating/paperwork, but you'd really get a lot more out of it once you have that minimum experience level.

Also a guaranteed interview, I'm still waiting for XJ to hire again.