GSP's certainly can be protective.
They are not as much so as breeds like the German Shepherd, and Dobermans when they are actually confronted, but the girls for sure can certainly sound like they will tear an intruder apart, and intimidate potential threats.
Naturally they won't defend with their life. They are a gun dog breed primarily to spot, point to, then retrieve wild game.
When it comes to guarding they are more inclined to try to corner the threat, and keep the threat in one place with displays of aggression, and moving into bite only when the threat does not stay where the dog wants them to stay.
So yes they are Territorial and protective like all dogs but have a very different techniques and methods to the guard dog breeds.
I grew up with female GSP's. The boys were a little harder to train as family pets, and my parents and grandparents preferred girls as pets and workers.