Hello everyone,
As legacy openvpn support will end with 26.1 version and openvpn instances will be the only way to connect to a server and to create a server, is there or more exactly will there be a way to choose the WAN in a multiwan for the openvpn client or sever. As for now it's only possible to my knowledge on the legacy mode.
You can specify a bind address in both, server and client.
However, remember that the clients outbound traffic obeys the OS routing table. If you want it to go out to another gateway, you have to redirect it with a policy-routing rule.