1) First of all: it's a provisional answer, depending on whether or not we're talking a) mountain gorilla or b) lowland gorilla. If b), then the gorilla would definitely win, seeing as the (Eastern) lowland gorilla is the largest of all the goriila subspecies. If a), then: all bets are off. Maybe the hyenas would win.

2) This is a rather Africa-centric question - why can't the gorilla be facing off against, say, a jaguar, or Komodo dragon, or perhaps even a Tasmanian tiger (true, this animal is extinct, but for the purposes of comparison, this probably wouldn't matter)?