I have a electric sliding canopy on my -8, however I didn't build it so I can't give you all of the details. but here is what I know so far. The electric motor is behind the rear seat headrest. Its a small motor with a cable loop like ironflight described. The size of the motor, well I don't know but I will look at it for you.
The latch system is still mechanical though. I am in PA if you interested in coming to see it. I will try to get some pictures for you, they will have to come later because we just got dumped on with snow
as for the safety issue, you can push against the motor pretty easily. There isn't that much resistance in the motor that prevents it from being opened the traditional way. You need just enough power to close it and open it, which surprisingly isn't that much. Like I said though my latch is the traditional one, also included is quick release pins on the rails to allow canopy disconnect in case of emergency.
ok soon as i can get out of my drive way, I'll get picks and video....