In my experience, guys will attend a co-ed baby shower if dad and mom to be are on board. Otherwise, you need to have girls only party.
If you go w/ a co-ed party, you may find it works well to do a few dad-specific gifts. Here is what we did for my BIL when he and my sister were expecting their first born: We did a tool-belt that we loaded w/ a diaper, travel-pack of wipes, small size of diaper cream, eye goggles, baby oil, and baby powder, safety pins, rattle, and toy. We also did an "emergency kit" with ear plugs, clothes pins (for his nose), and a few other things but I can't remember them all (you can search on line). Then there are cigars (we gave chocolate or bubble gum ones) that you can give to the dad to be to hand out. We also wrapped a few things for the baby that we specifically had Dad open (items with his favorite football team on it).