In theory you should be able to get a diopter to match your eyeglasses prescription and the Eyefocus system of the EOS 3 should word as designed.
I say "as designed" because this system works better for some people than others.
Did you dial in the calibration to the camera's memory as explained in the manual?
This calibration procedure is essential if the system is to work with your eye movement.
edit: I should mention the diopters are made by Canon and can be hard to find these days. I might have a -3 floating around somewhere if you find out your needed strength I can dig it up and we can figure if it will work out for you.
I no longer have an EOS 3 and the -3 was way too strong for me anyway.