3 WAN Connections and Firewall

Hi All,

I am looking for some design suggestions for our new setup.

Current: ISP A-WAN 1 and ISP-WAN 2
Firewall: x2 Meraki MX250 firewalls in HA (currently performing NAT)

New Setup:
ISP A-WAN1, ISP2 B-WAN2, ISP3 C-WAN3
We have x2 Peplink Balance 580’s purchased to accommodate the new setup in HA. Ideally i would like to have WAN 2 and 3 load balanced. WAN1 reserved for a specific VLAN however in the event WAN1 is offline, that VLAN failsover to WAN2.

Any ideas on how i can setup the balance to accommodate the new design?