Re: IPSec-VPN Backup Line on MPLS connection
That's depending on how traffic is routed through MPLS now. If everything is static, you need to have higher cost/distance static routes on the IPSec side for the same destinations. But if it's learning routes via routing protocol, generally need to use the same protocol over the IPSec but adjust some metrics not to prefer the backup side.
If static, you likely need to set link-monitor to detect a disconnection to the destination over MPLS and remove the primary static route.