Manual focus 20D
I have adapted a Pentax FB viewfinder magnifier for use on my 300D and 20D. It is a "straight-on" configuration
It requires some rework of its mounting hinge to make it fit on the Canon eyecup flange. The work is not complicated, but a bit tedious. (Needs some very small files.)
It does a great job. You can see essentially all the finder screen through it. It can be folded out of the way to look that the finder eyepiece directly.
Here it is at B&H: