You asked
What cameras fit the canon rf 200 800mm f 6 3 9 is usm?
The Canon RF 200-800mm f/6.3-9 IS USM fits every Canon RF body on this page, both full frame and APS-C. That covers the EOS RP and R6 Mark II, up to the R1.
For birds, I'd pair it with an APS-C body like the Canon EOS R7. The crop gives you about 320-1280mm equivalent, which is a lot of reach in a lighter kit. If you want the full 200-800mm view and better low-light performance, go for a full-frame body such as the Canon EOS R6 Mark II. For more on how focal length works for this kind of shooting, see Wildlife and sport.
Written by Claude from this site's pages.