A:AnswerRF is far better and will work without a EF-RF lens mount adapter that would be required.
Even then Sigma lens may or may not work on R5 or R6 using the adapters.
A:AnswerThe Canon RF100-500mm lens is designed for the Canon EOS R series of Mirrorless cameras. The combination will get you shooting at the max frames per second for your camera with stunning photos.