If I had to pick from the current crop of Hollywood directors for a big budget Guyver flick, I'd probably go with Guillermo del Toro. I think he'd be able to inject enough of his own creativity into the adaptation to make it digestible for the average moviegoer, while also maintaining the spirit of the manga. His work on Hellboy and Hellboy II should be proof enough of his qualifications.
This is all a pipe dream of course.