Here is a two parts Canon EOS R6 vs Sony a7 III full comparison review. The first part of the review is all about photography and the second one is about video.
Mathieu Gasquet published two excellent Canon EOS R6 vs Sony a7 III reviews which you can watch below. In this full comparison review of two full frame mirrorless cameras he discuss every possible aspect of both cameras, with plenty of comparison, sample images, and more.
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.