Is there any specific reason why your branch is not a separate network within your Org? This would make your life a lot easier when it comes to using AutoVPN and all of its beauties. If it really needs to be 3rd party VPN, https://documentation.meraki.com/MX/Site-to-site_VPN/Tag-Based_IPsec_VPN_Failover could prove useful for you.
... View more