Rouler works with network interfaces, so it isn't tied to a particular VPN. Use the official WireGuard client, Tailscale, Mullvad, OpenVPN or AmneziaWG, and run several side by side. If Windows has an interface for it, Rouler can send traffic over it.

A rule can match an app, a destination IP or subnet, or both. So one app can use different interfaces for different destinations. Your VPN clients keep running as they normally do, and there's nothing to import.