This is the first image of the upcoming Canon RF 100-300mm F2.8L IS USM Lens leaked online. It is scheduled to be officially announced very soon.
Canon RF 100-300mm F2.8 L has a relatively small impression for a large-aperture zoom lens up to 300mm through F2.8. It seems that there are voices expecting a built-in teleconverter, but as far as the image is concerned, it does not seem to have a built-in teleconverter.