HA Cluster with Port Aggregation

Hi

I  have a pair of Fortigate 100E and 4 CISCO 2960s and the requirement is to implement it with complete resiliency. 

2 switch are at upstream and 2 are at down stream.

Fortigate are configured in HA 

Support/advise is needed to configure port aggregation on Fortigate and Switches.

design snapshot is attached

Kindly advise.

Thanks