Here is a very exhaustive Canon EOS R6 vs Sony a7 III review. The review comes as two reviews: one is all about photography and one all about video.
Coming from Mathieu Gasquet, the two excellent Canon EOS R6 vs Sony a7 III reviews below discuss every possible aspect of both cameras, with plenty of comparison, sample images, and more. There is also a long and equally complete written review you might want to check.
From his conclusion:
The autofocus system and burst speeds are impressive, and Canon has out-classed Sony in its own territory with features like Animal Detection. The image quality is on par, if not slightly better, albeit with 20% less resolution. The image stabilisation is also superior (although not as much as the official specifications suggest) and I personally prefer the ergonomics, button layout and dials response on the EOS body.
As nice as the R6 sounds, there are some strong points in favour of the A7 III to keep in mind. It may not have 4K/60p or 10-bit internal recording for video, but it doesn’t suffer from overheating as severely as the Canon. There is a plethora of native lenses to choose between for the E-mount system, not just from Sony but also third-party brands, and that also means a better choice of affordable glass. Last but not least, the Sony is less expensive.
And here are the two video reviews. Enjoy.
Canon EOS R6:
Sony a7 III: