[chuachongchee]

Yea, this is a very simple link redudancy, a firewall is a firewall, not a load balancer...

Its a very simple active/backup link for your external interfaces to your isp, it cannot do a service based routing.

One way is as mcnallym pointed out, do static routes based on destination. This is manual, only good if your destination is known and doesn't change.

If you are looking at very dynamic incoming/outgoing link load balancing, i would suggest you to go for a dedicated external load balancer, like radware or f5..