Here's a hand I played last night at 1/2 in London.

UTG (~1200): Hasn't got out of line since joining the table
CO - Hero (950): Been card dead for a while so probably seen as tight
BTN (527): No real reads but he's on the waiting list for 2/5.

Pre:
UTG straddles to 4. Folds to hero who raises to 12 with Jd9d. BTN, SB, BB and UTG all call

Flop (60) Td6c8d:
Checks to hero who cbets 20, BTN calls, SB and BB fold, UTG raises to 90, hero calls, BTN calls

Turn (330) Td6c8d9c:
UTG checks, hero bets 175, BTN jams for 425, hero calls.

Not sure how I'm meant to play this hand, my main questions are:
1. Is flop sizing ok? I generally think betting small multiway in these spots works well but would be curious to know your thoughts.
2. Should we be 3 betting flop?
3. Does betting turn make sense and is the sizing ok?

If you choose this flop sizing it should be to induce a raise so you can 3bet.

Otherwise I'd go closer to 45, or as high as i think i can go and still get as many callers as possible.

Would really rather pile money in on the flop than see a turn if possible here.

Another benefit to 3betting flop is if btn happens to have a better FD here he is probably going to fold it.

Especially if there is any chance UTG has a folding range after his c/r this is a slam dunk 3bet. Even if he only has sets here we have enough equity to pile in with all the dead money.

Bet flop bigger and jam turn as played. Turn sizing is silly as you are giving hands like better flush draw or set a price they have to call, and you want more fold equity on both streets.

Whether to 3! Or call flop is a fairly complicated decision, and will come down to assumptions of what we think other opponents range is. I favor a call this deep.

PF - Live I like 4x as my standard.

Flop - I think most of your range likes big size on this board vs the others ranges so I don't really like the small size here. I'd go 45.

When UTG raises I range him at 88, 66, ATs, T9s-KTs(at 25%), 97s, T8s, 86s, Ad6d,Ad7d, Jc9c, KdQd, Kd6d, 7d5d.

You're 52% vs this range and being in position given your hand equity realization won't be an issue. So clear call.

When button calls his range is: Ad6d, Ad7d, Jc9c, KdQd, Kd6d, 7d5d, and maybe some T9, 98, 87 w/ bd and some 76.

Turn - I really think you should be checking here because you don't have many 7s compared to the 2 other villains.

But as played now getting 4.72 to 1 you only need 17.5% so it's a really trivial call even when half his range at this point has a 7 in it.

In my games, pre is too small, as it seems to be in yours unless you were just sweetening the pot.

Flop bet is too small. I'm not sure what you were trying to do? Did you want a raise? Because the deep stack raised, a call is fine, but I would have bet more or checked.

I actually don't love the turn be vs. two villains, especially considering UTG has us covered, but here we are. I'm glad UTG folded. Good call.

Flop flat is tragic

UTG has us covered. Are you raise/folding or raise/shoving? In reality (although unlikely), only a few of our outs are nuts.

check back the turn

Fair point Java, but I think UTG is wide enough from the straddle that we're big favorites and should just raise it up here pretty big. I think UTG straddler or BTN would have re-popped it preflop if they had many of the nutted Adxd hands and might have 3b their TT preflop too.

UTG has xr and I feel he would have fast-played his sets and gin-straights mw on this ddx board. Janda and all the recent book-writing gurus suggest playing a sfd like it's a made hand in these situations and I agree with their logic.

I'm raising the pot (at least) to iso UTG rather than pricing in the BTN with this call. I'm not folding to UTG or BTN either given that they can be so wide here so I suppose I'm going all the way.

$12 is a normal open in most 1/2 games and this is straddled. We're also very deep stacked so we want to build pots. $16 is my default here.

This board is way too wet to be c-betting so small. Also we dont mind taking it down since we only have J-high. I'm betting $40-$50.

As played check back turn.

Yep
Turn is awful for us