As you can see, there are a number of differences between these two cameras, many of which favor the Sony cameras. Even the less expensive Sony A7 III is ahead of the Canon EOS R in some important areas, such as the inclusion of in-body image stabilization (IBIS) and the lack of a 1.74x crop in 4K video mode. The Sony cameras also have higher frame rates with full-time autofocus (10 FPS versus 5 FPS) and dual SD card slots (although only one slot is UHS-II compatible). Sony’s popular Eye-AF system also works in continuous focus mode, unlike Canon’s that only functions in Single-Shot AF (AF-S) mode. So, on paper, both Sony A7 III and A7R III are the winners in most categories.
However, note that the Canon RF mount diameter is much larger than the Sony’s, at 54mm versus 46.1mm. The larger diameter, coupled with a 20mm flange distance allows Canon to have a large angle of incidence of 36.87°, which is more flexible than Sony E mount’s angle of incidence of 31.6°. This is far from a minor advantage (especially in the long run), as it gives Canon more flexibility in designing particular types of lenses, such as their new RF 50mm f/1.2L USM and RF 28-70mm f/2L USM that were announced alongside the EOS R. So, looking to the future, the RF mount has more flexibility over the Sony E mount, akin to the benefits of the new Nikon Z mount.
The Canon EOS R also fights back with its Dual Pixel AF, famously good for video work, as well as its full front / back vari-angle tilting screen – ideal for vlogging and similar applications. The Canon has far more autofocus points, too: 5655 (to the A7 III’s 693 and the A7R III’s 425). However, the number of autofocus points alone is not enough to say whether the EOS R will have the edge in focus speed and tracking ability, so it’s important not to read too much into those numbers. You’ll need to wait for reviews from production sample EOS R cameras to know how its autofocus compares to other options on the market today. Judging from lack of a proper joystick and use of the LCD for autofocus selection on the Canon EOS R, we can guess that the Sony cameras are likely going to be more user-friendly in the field.
In terms of video, it depends upon your needs, but the Sony cameras are perhaps slightly ahead on paper. Although both Sonys are limited to 8-bit output over HDMI, the EOS R’s 1.74x crop factor for 4K video and the lack of 120 FPS 1080p leave it handicapped compared to other options on the market (including both of Nikon’s newest Z cameras as well, as shown in our Canon EOS R vs Nikon Z6 vs Z7 comparison article). However, keep in mind that the EOS R has dual pixel autofocus and a 180 flip LCD, so for certain applications, the Canon does come out ahead.
Aside from that, the Sony cameras both have better battery life than the EOS R. In turn, the EOS R has a higher buffer than the Sony A7R III and a slightly higher buffer than the Sony A7 III, although the buffer capacities cannot be directly compared between these, since Canon EOS R has significant limitations for continuous shooting. The 30.6 MP resolution, of course, sits between the Sony cameras’ 24.2 and 42.4 MP sensors. The A7R III has a higher shutter durability than either of the other cameras, and the EOS R has a higher resolution rear LCD.
Otherwise, although there are a few differences here and there, the cameras are fairly comparable. They weigh almost exactly the same, and they all include features like Wi-Fi, bluetooth, and focus peaking. More minor specifications may lean in one direction or another, but those are the most important ones.