I have a gen4, but the hood mounting mechanisms should be the same.
It's really straightforward to replace the hood: 2 bolts on each side hold it in place, plus the struts if you have them. The latches are not under any kind of pressure, so no worries there, and the mounting bolts allow for some alignment, though I didn't have any issues with that. Two-person job, just because of the size of the thing.
Like tedmich said, get a new hood latch mechanism (held in place by 3 bolts, hood release cable connected to it), and figure out why your old one failed catastrophically to make sure it doesn't happen again.
As far as repairing your current one, you can pretty much forget about it, as it'll never look right. You should be able to bang it out to the point that it doesn't leak for now, but you'll need to replace it. There are quite a few of gen3 Camrys in the junks by now, so you might even be able to find a replacement hood in the same color to avoid having to re-spray.
Can also check http://car-part.com/
to see if there are any hoods locally.
Hope this helps.