Are you saying there is only a single pair of fiber between the sites? If so there is not much to load balance. Any traffic that goes to the one not connected to the fiber will have to traverse the one connected to the fiber anyway. It also means no redundancy since if the conected one fails there is no alternate path.
If they each have a pair of fiber then I would probably just configure a VPC between the two sites then configure the port channel interface with an IP address. If you do not like that option you can configure HSRP on both of them with the use of the "vpc peer-gatway" command so they will forward any packet bound for their neighbor.
