I opened UTG today with 99, and faced a 3bet from BTN, who 3bets IP vs EP 19% after 2.5k hands. I would 4bet GII with AK, QQ+ here, 4bet bluff some like AJo, but actually I have no clue what to do with those 77-JJ type of hands, same for AQs/AQo, AJs, ATs. 

How do you guys approach spots like this? I normally flat those suited broadways, but have no clue with those middle pairs.