we plan to use a router with 2 ADSL connections: 1 is dedicated for interface traffic only and the other is dedicated for VPN traffic only.
because ADSL connection gets IP and default route automatically from upstream router, there will be 2 default routes in the router,we can use policy based routing to manipulate the traffic and apply the policy on the ingress interface.
the issue is: I am not sure about the return traffic? is it return via the same path, or is it possible it will take another path back?
If the traffic leaving your router via the ADSL connection is NAT'ted to that interfaces address then the traffic will always return to the interface it left from.