There was the Canon EOS solution they published the beta for earlier this year. I have an old Rebel T5 that I decided to try out, even though official support bottomed out at the T6.
No capture card required, just the EOS Webcam utility and a USB connection. It runs very slowly, though. The latency is bad and so is the frame rate, though the picture itself is great. I've heard that reported for many supported cameras and varying computer specs as well so I'm not sure how long that will continue...