Hey, haven't been able to test it for hoi3 in particular, the classic multiplayer game move is to simulate a LAN connection through a VPN. That was my go to for minecraft and several other games for dirty fixes for a game or two with some friends. Not sure if there are better ones out there nowadays, but hamachi was always my go-to for free LAN through VPN games.
**Keep in mind though that free users can only connect with up to 5 people in a virtual network and that when you install it, there is some shovel-ware you might want to skip installing.