This is a BnM NL tournament I played in over the past weekend. It was early in the tournament. There were 15 of us and chip stacks were pretty even amongst us (somewhere around 1000). Blinds had just gone up to 50/100. The SB is unknown. First time I ever played against him. He seemed to be relatively loose/passive. Saw him call down a hand with middle pair. BB is my Dad and very well known. He will chase with mediocre hands preflop but if he misses, he'll throw them away. Here's the hand:

I'm in EP and get KK. I raise it to 300.
SB calls.
BB calls.
Flop is: 10h 2s 7c
SB bets 300.
BB folds.
I re-raise to 600.
SB calls.
Turn is: 8d
SB bets 300.
I call (all-in).
River is: Ac
Honestly, knowing what I knew about this guy, I put him on QQ or JJ. What hand would you put him on and why?