HA for WSA's is handled by the redirection method... eg WCCP, or PAC files, or a load balancer, etc. I think most people doing this use WCCP. The WSA's register with the router or firewall that they're there, and ready to take traffic, when one goes down, the router/fw sees that and just sends traffic to the remaining WSA.
1. for configuration sync between WSA's use SMA . SMA can manage WSA and collect reporting data from both WSA
2.when WCCP used and When a WCCP client fails, the portion of the load handled by that client is automatically redistributed to the remaining WCCP clients in the service group.If no other WCCP clients are available in the service group, the service group is taken offline and packets are forwarded normally (fail open)