Whew, detailed question. :-) If you're at networkers, run by the design clinic with this one.
Any routing protocol will be able to give you load sharing with this setup, since your links are equal cost. None of them are going to perform better in this department than any other. I wouldn't recommend ODR with this. You could use hsrp and split your groups so that half the hosts in one site use one link, while the other half use the other link. This would give you true reduncancy across the routers as well as some level of load sharing.
Other than this, I think you'll actually need to sit down with someone and work this one out--there are a lot of different ways to approach this problem in more specific terms.
Russ
