@muk
This is the "unique" soluction (or similar to this) if you want forced all LAN users to see only one IP on out,
and at the same time use also the other two connection for balancing.
If that's the only thing you care about, don't mistreat @anav
Pay a datacenter to host your own RouterBOARD,
make 3 VPNs, one for each WAN you have,
etc. etc. etc.
and so you can only show one (other) IP from the datacenter ...
It's obvious if you contact a site with 4.5.6.7, obviously the other party knows your address and responds to that, not another.
Or force all http/https/quik traffic to go over WAN3 and use the other two connection for the other services,
but the other IPs are still visible, if not on "myip", on all other services.
(and speaking of myip: 99% of the time it gives wrong answers ... It should be called "routerip" or "ispip"...
He hardly ever guesses the LAN address of the device he is launched into, because it is the only one that is really "his"...)