Opossum are good for ticks and sucks and they do not carry rabies or distemper like coons.
I would say your corn getting mowed down is groundhogs. I remember when I was little, dad had a beautiful corn crop of sweet corn, just days from picking. He came home 1 evening and it was all flattened, very little was eaten. He determined it was groundhogs. Just so happened we had a German Long Haired Collie pup that was 6 months old. By the next summer, you couldn't find a groundhog anywhere, that dog was earning his keep.