I've tried to find a complete list of all the EOS cameras using the T3 vertical release for remote shutter release. The only info I got was that EOS 3 was the first camera to use the N3 connector. This does not differ between the cameras that had no remote trigger socket and an actual T3 one (and possible other connectors). Is there a list of all the EOS cameras using the T3 vertical release?
There were several early EOS cameras that used the T3 connector for both wired remotes and to connect a vertical shutter release. Many of those early models are listed at this link that was current as of 1993. "compatible with T50, T70, T80 & T90 cameras as well as the EOS-1, EOS 5/A2E/A2, and the EOS 620/30/50/RT series when those cameras are fitted with optional grip GR-20"
The vertical release was only available directly from Canon Professional Services and was not distributed via the Canon dealer network. By the year 2000 the T3 vertical release was a rare, hard to find item.