Cap flop HU with middle pair +FD?

[synbad13]

I don't think there's much of a difference between capping and putting in 3 bets. Depending upon how aggressive you want to play the hand, you could cap the flop then check the turn. You could call his 3-bet, then raise the turn (he's much more likely to fold UI overcards on the turn).
I would cap the flop then probably bet (or call if he bets) the turn and check the river UI if given the opportunity.
If he continues to bet, then it depends upon what the board looks at the river if I still have a pair of 7s after all the cards are out.