Our loadbalancer are used to loadbalance Servers or Firewall, not link to ISP.
A router should be used for ISP loadbalancing as it requires to play with BGP.
Upstream loadbalancing is easy but it requires some special attention when an ISP does not want traffic with ip addresses from another isp to traverse its network.
So, check with the routing protocols/BGP experts.
A loadbalancer is definitely not the solution.
Gilles.
