As I know, a VPN connection can not act like/be/backup a trunk link. You can open up a question as "Backup trunk link over S2S VPN" in "Network Infrastructure" in "WAN Routing & Switching" section to make sure.
A workaround would be configuring Dynamic routing protocols with high costs, but that would not work if you have same VLANs at both sites.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...