You can mount pretty much anything on a m43 system using the right mechanical adapters, but that doesn't mean ergonomics are going to make it a practical option, specially on a camera with limited controls like the GF3.
You view through the viewfinder as with any m43 lens, but will be working in aperture priority mode. You can trigger manual focus assist, which will show you a magnified view of the focus area, but you will have to trigger it manually (unlike manual-focus m43 lenses like some Voigtlander models, where turning the focus ring automatically triggers MF assist).
In practice, using non-m43 lenses on a m43 body is not ideal. It's perfectly OK for landscapes, still lifes and street photography using estimated scale focus, but not anything involving action.