One IP with multiple gateway on WAN, howto?

[rexster]

i have 2 adsl modem router.
say, modem 1 ip 10.0.0.1
modem 2 ip 10.0.0.2
pfsense wan ip 10.0.0.10

all these connected on same switch and in same subnet.

so how can i do load balancing with this setup?

tia.
rex