The default configuration of a set of Cube Pro’s (wireless wire) is that of a “transparent” bridge, it should (and it does normally) work without any change.
There is normally no routing happening, so calling them “routers” is a bit confusing, you should consider them essentially as switches or bridges.
For reference, here it was posted a default set of configuration (“master” and “slave”):
http://forum.mikrotik.com/t/wireless-wire-cube-preconfigured-plug-n-play-doesnt/173973/1
It would be easier - I believe - if you start again from scratch and verify that the device work normally (with the backup 5 GHz connection enabled and without any other modification) and only once that is verified start fiddling with the bonding.
Otherwise, use this post instructions:
http://forum.mikrotik.com/t/forum-rules/173010/1
and post your current configuration (for both devices), it is possible that someone can spot where the problem lies.
Sometimes (actually often with Mikrotik configurations) the devil is in the details.