I'm not sure which Wein product you had in mind, but if you're hoping you'll magically get ETTL operation out of it, better stop hoping. The only thing you'll be able to do is to trigger the 420EZ. You'll have to manually set the flash power.
The most reliable 3rd-party triggering system is radio-controlled, like Pocket Wizard. Infrared systems like the Wein come next. Wein offers several different types of infrared systems, some with coded signals to prevent spurious triggering. You'll need a transmitter that usually goes on the camera's hotshoe and a receiver that connects to the flash.
Because the 420EZ does not have a PC sync connector port, you'll need a female hotshoe adapter with either a PC sync port or a miniphone plug if you decide you use Pocket Wizard.
Frankly, none of this is worth the trouble. A Wein wireless system will cost as much or more than a 420EX flash which will work perfectly with the 20D, ETTL and all. I would only go the wireless route if you want to use the 420EZ as a supplemental, off-camera flash for studio work.