Can OpenVPN do site to site VPN?
With OpenVPN Access Server, a site-to-site VPN is as simple as connecting your router. You first set up Access Server at your headquarters, then each additional location is set up with a router that has a user connection profile.
Does OpenWrt support OpenVPN?
This is available from OpenWrt 19.07 onwards. All self-respecting commercial OpenVPN providers will offer self-sufficient OpenVPN config files you can load in your consumer router or network appliance to connect to their service. You can use them in OpenWrt too.