Sony A6500 or A7iii to photograph whales underwater?

I sure would prefer to have all optics and camera bits on board with me in carryon, but the stuff is just too big.   My roller bag fits under a seat, by the way, at least if I end up with a full size underseat area.  In those small planes, I have to resort to that, but in those planes I also think I have less risk if the bag has to get gate-checked.

My alternative is to use the Thinktank backpack instead of the roller bag, because it would hold more gear.  But even then it would not hold everything, and then I'd have to carry it (plus the waist bag), which has just gotten too heavy for me at age 65.  As it is, I put the most expensive gear in the roller bag, and pad the suitcase as much as I can.  Considering I have a 36-quart flexible cooler and a neoprene wetsuit, as well as a BCD and fins, I can pad things up pretty well.   I stick the laptop inside the cooler for extra protection.

Here is the out-of-camera shot before Lightroom.

And again, after:

White balance using eyedropper tool on the metal in the mouthpiece, I think.  Possibly on some black part of the gear.

Various edits to reduce highlight glare and boost shadows.   I do this a lot - reduce the recorded dynamic range as desired.  I select a profile to apply in here too, usually Camera Standard.   I overboost the shadows a bit in anticipation of using the black slider.

Done judiciously, the black slider makes that 'haze' vanish, at the expense of lost shadow detail.   Once you are near the edge, a small bit of movement (of the black slider to the left) can push you over the edge and much the whole shot up.  Before the black slider, the shots looked almost the same for haziness, though the subject looked pretty good.

That was Connie's last dive, and the last underwater picture I ever got of her.  RIP.