@David Ramirez Rodriguez Thank you for reaching out to Microsoft Q&A.
I understand that you are having questions regarding setting up S2S VPN over ER and S2S VPN over Internet both from the same on-premise as primary/backup solutions.
This is defintely possible to setup but you need BGP enabled on both the tunnels and you need to advertise the same networks on both of them. Please note that the S2S VPN over ER will always be preferred as it will have lower number of hops. Hope this helps.
Please let us know if you have any further questions and we will be glad to assist you further. Thank you!
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