Body upgrade advise (1 Viewer)

I am currently using 7D with Tamron 150-600 G2 for birding having downgraded from Canon 500mm 4.0 L IS due weight limitation on my physical body. I do a lot of birding under tropical rainforest thus my biggest problem is focus lock due to stronger back light and low lighting.

Which body would best handle the above? Shooting speed (FPS) isn't an issue. I have the following I mind. 77D, 80D, 7D2, 5D3 or other higher cost camera as used or refurbished. 1 series not considered due to weight factor. I still have my 1.4X Extender III.

My recent downgrade shed some weight off including a 70-200 4.0 L IS for those big birds popping out the corner. Friends had suggested going the MicroFour Third way but I wasn't done with Canon yet as I still have a cabinet full of Canon gears, including my wife's birding gears.

Any suggestions/recommendations will be greatly appreciated. Thanks.

If lighting is an issue then check which bodies operate best at higher ISO. My guess would be the 5D3, however you may still prefer a cropped sensor for the extra magnification you don't get with full frame.

Difficult choice, not sure what to recommend 100%.

After a while without getting any response, I posted at another forum. There it was suggested that I should get a 5D3 or 5D4, both used to suite my budget. Then someone suggested I take a look at Sony mirrorless. Their newer mirrorless are such a fantastic performer at a lower than comparable Canon model. Also, the mirrorless technology is moving very fast thus I was advised to hang on my current gear, start saving and dive into mirrorless bodies. DSLR would be dead or near dead very soon.

The current adaptors to use Canon glasses are still an issue but expected to improve drastically soon. Hopefully they would have resolved these by the time I saved enough.