Adding a bit to Ram's.
When provisioned for L3 discovery, the APs will always try to connect to the controllers in the provisioning order. For example you provision APs in group A to associate with manager and APs in group B to associate with member, you'd configure the provisioning for group A in order
10.0.0.1
10.0.0.2
For group B you'd configure
10.0.0.2
10.0.0.1
Please note that even when configured this way, the APs may in certain circumstances end up managed by the "wrong" controller. An example; an AP in group A is coming up but there's a disruption in the connection towards the manager but the member responds, the AP will associate with the member. Once connection to manager is restored, it will not migrate to the manager. However which controller is managing the APs seldom matters.