Hello,
I would suggest using different IP subnets and letting routing protocol
handle the load balancing. If you bridge the interfaces, there is a chance
that you create a loop in the network. Also, if it is bridged, the
interfaces will participate in spanning-tree calculations. So, every time
some change occurs in the network, your router interfaces could be down for
about 30 seconds (spanning-tree calculation time).
Hope this helps.
Regards,
NT