I've been considering a similar switch, and I think maybe the R7 has the edge here for a wildlife shooter, but I do agree, it's difficult to decide between the two, and they're pretty evenly matched, since both cameras have:

• Digic X processor
• animal eye detection/tracking autofocus
• in camera focus-stacking [handy for flower macros]
• very high burst rates 30 fps/40 fps between R7 and R6 II
• dual card slots
• IBIS
• a joystick
• dual-wheel prosumer controls
• they're close on size/weight
• articulated LCD

Both, however, lack a pop-up flash. And neither has a top-deck LCD, things you may be used to having on your 7D II.

Sidenote: most folks are trying to decide between an R8 and an R7, given that they're both the same price in the US ($1500, body only). And in that case, it's more R7 for the features (IBIS, joystick, dual card slots, in-camera focus stacking etc.) vs. R8 for the full frame.

Why the R7 might better:

• Higher resolution (33MP vs. 24MP). While this will lower dynamic range and high ISO noise performance, for a wildlife/bird shooter, being able to crop with less detriment is always a bonus.
• Crop factor can help you achieve more apparent "reach" with shorter/smaller/cheaper lenses than crop. On full frame, all your lenses look 1.6x shorter. So, say, the RF 800mm f/11 DO IS STM on an R7 will have 1280mm equivalence; and the RF 100-400 f/5.6-8 IS USM has 160-600mm equivalence.
• Lower pricetag new (US$1500 vs. $2500) so you'll have $1k more to spend on lenses.
• Easier to find on the used market and refurbished (at least here in the US at this moment; a refurb R6 II is back ordered, while the R7 is in stock).

Why the R6 II might be better:

• Full frame (though this can also be more of a PITA for wildlife/birding (needing 1.6x longer lenses to frame equivalently) and macro (thinner DoF, because longer lenses or shooting from closer)
• Of the 30 or so R-mount lenses Canon has released at this time [Sep 2023], only three of them are RF-S (crop-specific). The array of native lenses is far more complete for full frame. While a crop shooter can use full-frame lenses; right now there are lenses you can get for R full frame you cannot get for R crop: an ultrawide zoom, a pancake lens, and an f/2.8 walkaround zoom. Yet.*
• The AF performance will be stickier/faster, because the R6 II has faster sensor readout, and with mirrorless, there's only one sensor doing all the work of image capture, metering, and autofocus.

*This is likely a temporary situation; remember Canon has EF-M crop mirrorless optical designs to leverage. If you look at the three RF-S lenses, they appear to be tweaked versions of EF-M designs. The RF 18-45 from the EF-M 15-45, the RF 18-150 from the EF-M 18-150, and by extension, the RF 55-210 from the EF-M 55-200. Which is probably how Canon could release all three lenses in one year. If Canon "ports" the EF-M 11-22 and EF-M 22/2 pancake designs to RF-S, then two of the three missing types are ticked off the list. However, Canon never made an EOS M f/2.8 walkaround zoom, so it's likely starting from the EF-S 17-55/2.8 design would take more time due to the greater mount depth difference. But if you need one of these types of lenses right now for an R crop body, your only option is to adapt EF-S lenses like the 10-18, 24/2.8, and the 17-55/2.8.