Duadl site dual WAN failover and load balancing

[epilas]

Hello everyone. I have two sites with one pfsense box each. Each pfsense has two WAN connections to an ISP all with static IPs. What i want to achieve is have a VPN between the two endpoints with failover and load balancing.I am using pfsense 2.1RC0
I have seen various ways of doing so and i really cannot decide what is the best to do. So my questions are the following.

1. If i setup GRE tunnels (with or without IPSEC?) will i be able to run OSPF and use all of the available  links?
2. is it better to setup site to site OPENVPN and then run OSPF on the OPENVPN interfaces?Still will the load balancing work?

It is crucial for me to have load balancing because the upload speed is just maximum 1024Kbps (adsl).

Thanks a lot in advance for your help.

Attached is my topology