Max Hoopa needs to watch some more discovery. He's obviously unaware of salt water crocodiles and the fun fact that that three species of sharks can live in fresh water, most dangerously bull sharks which can attack people.

Are we talking about living animals or anything from history?

Living animals is easy salt water crocs versus a great white, the white wins. It happens croc corpses have been found with great white teeth in them and giant pieces missing. Obviously not a predation attack, the croc must have done something to get the shark to attack since the shark didn't eat it.

We dig in history and Megalodon and Sarcosuchus are the biggest of their kind. I'd expect the same result. Never happened since they lived in different eras but Sarco was twice the size of modern crocs, Meg was double or triple as big as a great white.

Since one is a fresh water animal and the other a salt water animal they are unlikely to meet.