I'll take a stab at this one.

EDIT: The posts below mine offer good responses that are contrary to mine – I may easily be wrong about everything I say below.

A close decision between shoving and 3bet/calling, as you said.  I would hope to lean towards shoving.  It may be ok to just flat preflop too to keep the pot small but I would rather do that on the button.

The reason I lean towards shoving is because when 3bet/calling, the preflop decision is easy, but I actually would not be happy if he called (which he might because he has position) and if the flop was remotely bad.  I don't think it's actually best to shove any flop, and if it is best, I'm not too happy about it.  

If the board hits us with AK, I would rather be all in already then have to try to get it all in.  If he has KK, and the flop is AXX, he will certainly fold if we shove on the flop, and if we check the flop he might not bet.  It would be way better to be all in already – same thing goes for if he flats with mid pairs or any AX-AQ. He might pay us off with AQ if we shove the flop, but he definitely will if we check.  A9s-ATs are hands we want to have betting into us on this flop, and probably will if we check, but won't call a shove.  All missed pocket pairs on the AXX board may or may not bet on the flop if we check, but they won't call if we shove.

There is an argument for 3bet/calling because if we 3bet, he calls and the flop is AXX, he may have folded if we shoved preflop and we would have lost out on chips by shoving.  But this seems to be the only worse thing about shoving and it's not going to cost us that much compared to possible winnings from shoves.  

When we 3bet and he calls, we''re up against his open/call3bet range, which is the middle section of his opening range between open/fold range and open/jam range and of course it may include AA/KK type traps.  These medium strength hands that he''s open/calling our 3bet with are not likely to donate their whole stacks on the flop when we hit, especially if we are jamming the flop (whether it's any flop or good flops).

When we shove and miss out on chips from those hands that would have called if we 3bet, we usually miss out on less than 1/3 of a stack (less because we're still gaining the 700 from the current pot).

When we shove and get stacks in against those hands that would have called our 3bet but would fold on the flop, we are often awarded an extra 2/3 of a stack.  

The times we lose because we shove and get beat, we only would have been better off 3bet/calling preflop if we were not going to shove any flop.  If he decides to flat with a decent to strong pocket pair and we miss, we''re not in any better or worse shape than if we had shoved preflop unless are now able to save chips on bad flops by not shoving. This comes close to a fit or fold mentality, which is part of why I wouldn't want to 3bet and be called here.

If I had a very loose 3bet/fold image or if I had to recently show down something weak after 3betting, or if my recent pattern suggested for some reason that I would fold after 3betting,  I may lean more towads 3bet calling.

In general I would hope to shove this until up to like 28BB .. If 3bet/calling, I don't think it's a mistake, but I''d be cautious on missed boards.  Check/folding or check/assessing weak bets from villain is probably better than shoving on the flop.  I wonder what the pros say about flatting preflop too.

Please note I am not a coach/vidmaster, and maybe a coach/vidmaster can correct what I say.