I haven't seen Inter parking the bus against a team for a long time. They have been used to playing with 3 defenders and an offense-oriented game at the same time.
But you forget that Inter played 5 defenders in a 3-5-2 formation against Milan in the semi-final second leg. Denzel Dumfries and Federico Dimarco played more advanced but they were able to integrate into a 5-3-2 formation when the opposing team was building up attacks. The same scheme will also be implemented by Simone Inzaghi against Manchester City in the final, so I think the 3 defenders are just a fake formation.
Simone Inzaghi is fully aware of how dangerous Manchester City can be in attack, so he may really need to work out the best strategy throughout the game. However I have no hesitation in saying that Manchester City will do something great in the final even if Inter want to fight with all their might.