Multiwan Multi RB failover & load ballance

Greetings

Heres my setup:

What I am trying to do is to get WAN1 & 2 to RB#3, then create load balance & failover, which I can do if all WAN1-3 were on the same RB

I just need a pointer in the right direction, I am new to routerOS.

Sofar, I think one should make a (bridge/IP tunnel/??) between RB1->RB3 and RB2->RB3 onto an interface on RB3, afterwhich I can do the load balancing and failover based on the interface, pointers, wiki src ?

Would using SXT Lite as the Wireless bridges make life easier as it will be routerOS throughout? or can any vendor for the bridges be used as it does not matter ?

Thanks !!

StormEc