If you want to load balance wan connections take a look at the following wiki entry:
http://wiki.mikrotik.com/wiki/Load_Balancing_Persistent
However in your case you will need to use
masquerading instead of
source nat and you will need to use
interface routing instead of
next hop routing.
I.E. instead of:
/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 scope=255 target-scope=10 routing-mark=odd
add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10 routing-mark=even
you would use:
/ ip route
add dst-address=0.0.0.0/0 gateway=wan1 scope=255 target-scope=10 routing-mark=odd
add dst-address=0.0.0.0/0 gateway=wan2 scope=255 target-scope=10 routing-mark=even
and with NAT, instead of:
/ ip firewall nat
add chain=srcnat connection-mark=odd action=src-nat to-addresses=10.111.0.2 to-ports=0-65535
add chain=srcnat connection-mark=even action=src-nat to-addresses=10.112.0.2 to-ports=0-65535
you would use:
/ ip firewall nat
add chain=srcnat connection-mark=odd action=masquerade out-interface=wan1
add chain=srcnat connection-mark=even action=masquerade out-interface=wan2
let me know if that helps