You asked about defending against ep open raising with 77+ (e.g., 77, 88, 99?) when you are holding KJs or ATs right? If you know that the villain's range includes middle pairs, it seems to me that you're in pretty good shape with your cards. When the flop comes with some of A, K, Q, J, or T (which it often does), especially if two are the same suit, he's going to have a tough decision what to do if you bet out right away on the flop. If he just calls, you're generally good for another bet on the turn. As long as he doesn't land his set, he's going to then have a really tough decision to make after your turn bet.
On the other hand if he re-raises you on the flop, he could have the AQ combo, in which case you just fold (unless you've got a good OESD/flush draw).
I wouldn't 3-bet and I wouldn't fold pre-flop to an open raise if I have reasonably good cards. I would just call and trust in my post plop playing skill.