@ kubiko look here:
http://forum.mikrotik.com/t/dual-pppoe-wan-failover-with-specific-port/181541/8
table main
/routing table
add fib name=to_WAN_main
/ip route
add dst-address=0.0.0.0/0 gateway="20.30.40.49" routing-table=to_WAN_main
/routing rule
add routing-mark=to_WAN_main table=to_WAN_main
add src-address=20.30.40.48/30 table=to_WAN_main
table bkp
/routing table
add fib name=to_WAN_bkp
/ip route
add dst-address=0.0.0.0/0 gateway="60.70.80.89" routing-table=to_WAN_bkp
/routing rule
add routing-mark=to_WAN_bkp table=to_WAN_bkp
add src-address=60.70.80.88/30 table=to_WAN_bkp
default gw
/ip route
add dst-address=0.0.0.0/0 gateway="20.30.40.49" distance=1
add dst-address=0.0.0.0/0 gateway="60.70.80.89" distance=2