The-Digital-Picture added the Sony a7RIII and Sony a7III to their resolution comparison tool and it allows for an interesting comparison between the Sony a7RIII, Sony a7III, Canon EOS 5Ds R, Canon EOS 5D Mark IV, Canon EOS 6D Mark II and more. The tests linked below were all performed with the Canon EF 200mm f/2L IS USM.
Sony a7R III compared to the Sony a7 III
Sony a7R III compared to the Canon EOS 5Ds R
Sony a7R III compared to the Canon EOS 5D Mark IV
Sony a7 III compared to the Canon EOS 6D Mark II
Sony a7RIII: B&H Photo / Amazon / Adorama
Sony a7III: B&H Photo / Amazon / Adorama
Canon 5DS R: B&H Photo / Amazon / Adorama
Canon EOS 5D Mark IV: B&H Photo / Amazon / Adorama
Canon EOS 6D Mark II: B&H Photo / Amazon / Adorama