$25 NLHE 6-max: rush, nl25 - KQo, preflop and river?

Full Tilt, $0.10/$0.25 No Limit Hold'em Cash, Rush, 6 Players

Hero (BTN): $48.21 (192.8 bb)
SB: $48.41 (193.6 bb) 20/17/5 2.7k h
BB: $28.37 (113.5 bb) 25/20/5 300h
UTG: $17.87 (71.5 bb)
MP: $19 (76 bb)
CO: $55.84 (223.4 bb)

Preflop: Hero is BTN with Q K
2 folds, CO raises to $0.75, Hero calls $0.75, 2 folds

Flop: ($1.85) 7 3 K (2 players)
CO bets $1.11, Hero calls $1.11

Turn: ($4.07) 8 (2 players)
CO bets $2.44, Hero calls $2.44

River: ($8.95) 2 (2 players)
CO bets $7.16, Hero ??


Info on villain:
So first question is about preflop. Is this a clear 3bet for value vs particular opponent? I decided to simply flat and not bloat up the pot. If there would be aggro regs behind i would prefer to 3bet myself.

Flop and turn are quite straight forward in my opinion.

River is a bit interesting. He changes his betsizing on the biggest blank that is possible. Whats our play and what he is trying to tell us here?

When you simply just keep calling your getting no info. And he can safely assume his 2p or even TPTK is good.

I think against this player you probably have the best hand pre-flop so maybe I wouldn't 3bet. I think he just wants to see a lot of flops so he might fold the worst hand pre-flop.
I think i would have raised the turn and fold to a re-raise so i can control the pot on the river and so i have a better idea where i am at the hand.

It's still a pretty small sample, but based on his stats, he is bluffing the river frequently. He has 100% river cbet, 44% river AggFrequency, 36% went to SD, 39% won$ at SD, as well as a very wide opening range(57%); all of those things tell me to call. That said a sizing read is often a better tool than HUD stats. It looks like an ambitious value sizing to me, but when I consider his turn and flop sizing, it doesn't make much sense unless the river deuce improved him, which seems really unlikely. Anyway, I definitely call here, barring a very good read on his bet sizing.

Based on his stats he looks like someone who gets pot stuck a lot. I'd raise the turn though, but as played, call the river. I don't think you have enough info or history to justify a next level play and raise the river.

I'm not good enough to raise the turn, but calling the river doesn't seem difficult. The river card is about as blank as it gets, and it seems like too much of a stretch to change from thinking we're ahead on the flop and turn to believing we're priced out to call the river just because he changed his bet size - not unless he has shown such a betting pattern before.