I've just completed the latest round of GAC in a draw 836 - 836.
It was my first time therefore I just looked it up and found out highest GP wins as stated here:https://forums.galaxy-of-heroes.starwars.ea.com/discussion/189892/grand-arena-tie-breakers#latest
I think there should be an exception for when a full clear of the territories happen.
My opinion is that the first one to clear all territories should get the win when there is a draw.
To me it would make much more sense in terms of the spirit of competition.
I think it only makes sense for when there is a full clear of all territories.