i want to load balancing multiple adsl. this is my situation:
multiple adsl in BRIDGE MODE connected to a switch and a RB connected to that switch too.
i have multiple pppoe interfaces (one for each adsl)… how can the pppoe interfaces dial trough the correct modem?
is that possible?
am i clear?
Unless I am misunderstanding your physical layout this is only possible if the switch is VLAN capable. If it is, just hook the modems into one dedicated VLAN each, add all four VLANs to the uplink port to the router, and attach the PPPoE clients to the VLAN interfaces.
You could use a RB750 , it could load balance 4 adsl modems (one per ethernet) and one ethernet for output to switch with no issues. (and they’re cheap) 
+1 to what fewi & Nitrious said.
You either have to use unique VLAN’s (like fewi said) / unique Ethernet ports (like Nitrious said) for the modems
OR
you can dial a PPPoE connection on each modem and then perform NAT on the ADSL modems.