But yeah, animal fights.... Always go with the animal that weighs more.
Gorilla v. Lion:
Similar weight, if they fought just one on one in a neutral terrain. I'd go gorilla in a very close match. Stylistically i think the gorilla could get his hands on the lion and thats where the gorilla's super crush strength becomes a bigger factor than the lion's slashing claws. Chimpanzees can lift broken trees dead lift style, and Gorilla's are much physically stronger.
Its been observed that Lion strategy is typically a rush in get you on the ground and bite you on the neck style where they plant their feet heavy. Their objective is always to ground their opponent before trying to finish them off Lion-Juijitsu style. But thats kinda like Matt hammill trying to take down Rampage, before going for the Rear naked choke. Good luck getting the takedown Lion.
Tigers have shown that they are lighter on their feet than Lions.Source
and tend to fight with a more sprawl-and brawl strategy, striking heaviliy on the outside. Now stylistically, i think Tiger beats gorilla all day on the outside. This is because if niether fighter is intending to take the fight down(2 sprawl and brawlers), the faster more technical striker is likely to do more damage. See Machida v. Rampage, but imagine if Rampage didnt have a gameplan, and instead just went ape-****(pun!). Another example that would work is Liddell v. Rampage.
But yeah - Gorilla v. Lion - Gorilla via stoppage, broken spine.