need help configuring failover/load balancing

I am a wisp and have a second small tower servicing about 15 - 20 users. I have 2 access points on my main tower and have 1 gateway for the whole system.
What I would like to do is have a mikrotik router with a ocnnection to the the main tower from each of the access points be load balanced to offer service to the second tower.

Tower 1
AP 1
AP 2


Tower 2
microtik - ClientAP1

  • ClientAP2
  • AP 3 servicing tower 2

I would like AP3 to load balance to Tower 1 through client ap1 and client ap2 which are just bridges to the respective APs. And if AP1 or AP2 goes down, I would like it to failover and just use the one that is still up and running.

If you need any clearification, please let me know. I have ordered a Routerboard 532