Yes. Since the Canon 20D does not have live view, an external monitor will only help if it can display the camera’s playback output; it won’t give you modern live-view focusing. In practice, the most useful field option is usually a portable image viewer or a tablet/card-reader workflow.

Options mentioned by users include:

• a portable photo storage/viewer that accepts CompactFlash and allows zooming into JPEG/RAW files to check focus
• a tablet such as an iPad or Android device with the right card adapter/reader
• recording to SD via an adapter, then reading that card on a tablet
• wireless transfer solutions such as Eye-Fi cards, if compatible with your setup

A standalone field viewer is the closest match to what you asked for because it avoids carrying a laptop and is designed for image review and backup. A tablet plus card reader can also work well if you already own one.

So: yes, there are workable larger-screen review options, but for a 20D the best path is usually viewing files from the CF card rather than expecting true live-view output from the camera.