Site-to-Site force tunnel to use gateway group rather than default gateway

[l3rady]

I have two WANs.

WAN1 - Default gateway - dedicated leased line
WAN2 - Faster line but not dedicated.

I have a WAN_FASTEST gateway group, set up in failover from WAN2 to WAN1, that I want my WG site-to-site tunnel to use however it is using the default gateway.

I have DDNS setup on this group and the remote peer is using an endpoint hostname that does resolve to WAN2 currently.

I've followed this guide to get the site-to-site working: https://docs.netgate.com/pfsense/en/latest/recipes/wireguard-s2s.html

All is working fine but I cannot get the traffic to go over the gateway group.

I've tried changing the WAN FW rule to policy routing by setting WAN_FASTEST as the gateway and doing the same on the allow-all rule on the WG tunnel.

I'm not sure what else I can do? I know I cannot use a static route as you can only push to one gateway, not a group, and also that won't work as the remote-end is dynamic, using DDNS, and won't accept a hostname.