sonertari
commented
3 years ago I have never used wireguard, but I see that OpenBSD supports it: wg(4).
I have configured multiple wan connections on OpenBSD (your requirements seem similar), but it's been 15 years. I don't remember the details, but I know that what you describe is possible, so I think all you need is in pf.conf(5). For example, you can write pf rules to use the same wan interface for both incoming and outgoing packets of a connection, see the reply-to option in pf.conf(5). I remember using queues to prioritize certain network traffic too.
All of these are thanks to OpenBSD and pf. PFRE on UTMFW may help you learn and configure pf, and you can configure network interfaces on the WUI, but you may like command line better, as you wish.
Does this support Wireguard for VPN? Does this support MultiWAN (multiple wireguard connections), meaning having multiple public IPs, for which incoming traffic are accepted, then sent to a port on a internal server. Here its also important that the resulting response traffic, is emanicated from the correct WAN interface, so WAN1:80 might be assigned to 192.168.1.10:80, and WAN2:80 might be assigned to 192.168.1.10:81. Response traffic with a source of 192.168.1.10:81 must be sent out from WAN2:80, even tough default gateway is WAN1.