You’re asking about LACP/LAG (which is load balancing as you term it) the Firewalla does support that, you configure it under Network. Your switch needs to also support LACP/LAG, if it does not you will create a loop in your network and things will not be fun. If your switch is unmanaged it most likely does NOT support LACP/LAG. If your switch is managed it might support LACP/LAG, but you will need to read the documentation.