Back in April, Canon published the first specifications for the upcoming EOS R3, but said practically nothing concrete about the upcoming video functions.
This has now changed - among other things because Canon has now released its own 
teaser website for the EOS R3 with more information. We still don't know anything about the concrete resolution of the camera's new BSI sensor, but it is supposed to enable "4K videos with Canon Log 3 support, oversampled 4K as well as internal RAW film recording".
In fact, the R3 is unlikely to be much lower in video specs than the EOS R5, which is also capable of full sensor downsampling (from 8K to 4K HQ up to 30p), Log 3 and internal RAW.
Since Canon is implicitly targeting sports photographers with the R3, we can assume that the sensor will be a fast 5-6K sensor rather than a ponderous 8K sensor. Personally, we would now also heavily assume that the R3 will offer at least full 4K downsampling at 60p. Possibly even more, since Sony already offers 120p here and sports photographers are probably also attracted by high slow motion frame rates in video recording.
Besides the upcoming video specs, Canon has also announced other new features:
For example, the EOS R3 is said to offer improved AF performance and tracking capabilities using Deep Learning technology. In addition to even better face, eye, head and animal body recognition, vehicle motive detection and tracking for cars and motorbikes is also to be added.
The optical image stabiliser is said to be able to compensate for up to 8 f-stops through a combination of sensor and lens, while the autofocus promises to be able to focus "up to EV-7".
For high-speed image transfer, the EOS R3 will feature Wired LAN (i.e. Ethernet interface) and 5GHz Wi-Fi. The new accessory shoe should offer further options for data communication and power supply, while also supporting new accessories. Can we hope for external XLR connectors like those of the competition?
The following specs are already known:
Dual card slots: 1 CF Express, 1 SD.
LP-E19 battery
Magnesium alloy body
Adjustable touch LCD monitor
;)