/ip firewall mangle
add chain=input in-interface=wan1-out action=mark-connection new-connection-mark=wan1
add chain=input in-interface=wan2-out action=mark-connection new-connection-mark=wan2
add chain=output connection-mark=wan1 action=mark-routing new-routing-mark=wan1
add chain=output connection-mark=wan2 action=mark-routing new-routing-mark=wan2
/ip route
add dst-address=0.0.0.0/0 gateway=10.0.0.1 routing-mark=wan1
add dst-address=0.0.0.0/0 gateway=10.0.0.2 routing-mark=wan2