Regarding ISP failover, you can achieve it using BGP.
About sending traffic to particular ISP, you can define RG groups and keep the priority high for the node from which you want to exit the traffic. For example suppose your VoIP traffic is originating from reth 1 and this is linked with RG group 2, on RG 2 just simply defining hight priority i.e 200 for node 1 will help to exit from node 1.