You can do a GPR even with limited endo experience, but will make your app solid for an endo residency as they don't take too many new grads.
just anecdotal, but I have friends that got in to endo that did GPRs at the following places: Ohio State, OHSU VA, AT Still AEGD, Illinois Masonic.
I would probably look and see if there is a staff endodontist at the program, but I don't think it matter quite as much which AEGD/GPR you do as much as it matters that you do one.