The Canon EOS RP is currently the cheapest full-frame mirrorless camera on the market while the Sony a7 III is the best selling full-frame mirrorless camera according to Amazon sales. If you have to choose one of them and stuck between Canon EOS RP and Sony a7 III.
The Slanted Lens has compared the Canon EOS RP with Sony a7 III, check out the video review below.
On the contrary we think the Canon EOS RP is more entry-level FF MILC then the Sony a7 III and they are not in the same league. Your choice is depending on what you need and the price. Hope this Canon EOS RP vs Sony a7 III comparison review helps you find the best gear for you.