Curious why you chose OpenVPN for your site-to-site links. I use it extensively for mobile VPN users, but for an "infrastructure" VPN, I use IPsec, which I find to be a much superior solution for that use case than OpenVPN.
Beyond that, pretty much every router out there supports IPsec, so if you're needing to integrate with other non-pfsense hardware, IPSec is often your only option.