Splitting traffic between two network adapters

I have a desktop with two Ethernet adapters. I would like to send one type of traffic down one cable, and another type down the other. I understand this type of filtering can be done at the router, but my goal is to do it on the desktop before it even hits the router.

I know I can add routes and configure the metric of those routes to give priority. However, I want to filter traffic based on protocol.

Problem:

-- I use a VPN service and would like one Ethernet adapter to send all VPN traffic out of that interface

-- I would also like to use my second Ethernet adapter to send "other" types of traffic (Internet browsing) which is not tunneled through the VPN

I read about split-tunneling, but was unable to find something relevant to my case. I think I'm close, though, just need a nudge in the right direction.