Answer:
Well we need to look at their advantages, their abilities.
Explanation:
Medusa can turn anyone to stone, all they have to do is look in her eyes. She also has snakes for hair. No one knows what type(s) of snakes. If the snakes are poisonous, then she has another advantage, the snake could poison Cerberus. If they aren't poisonous then they can only wound him.
Cerberus is a 3 headed dog and dogs don't make eye contact. It's rare they do so it would be unlikely that medusa could convince Cerberus to look in her eyes. Cerberus lives in the Underworld, as a pet for Hades. He is used to toxins and so certain types of venoms/toxins may not affect him. No one knows what type of dog Cerberus is but many suggest he is a form of Hellhound. Some say Hellhounds can shadow travel and withstand fire. If Cerberus is a Hellhound he could use fire and shadow-traveling to his advantage.
It is hard to tell but if it came down to betting on who would win, I'd bet Cerberus because let's face it, Hades isn't gonna let something bad happen to his pupper, who would?
