You have AA in the BB. The BTN opens to 3.5x. What is your line ?
The standard line would be to re-raise to what ever your defend re-raise is.
Depending on how often the BU raises you should be defending with a re-raise a decent range. If you defend with 88+ and sometimes just suited connector then AA will not stick out. Just call with some of your re-raise range sometimes but I would always re-raise AA here.
Give them a chance to re-raise you back in case they have a real hand like KK so you can get it all in. I have read never slow play the nuts as your opponent might have a hand willing to come along.