You could have all your ports on your windows firewall open and it wouldn't make a difference in reality,
your router's firewall is more important, and all ports should be disabled by default on there anyway.
i mean it would work for p2p connections in theory.
but yea one solid connection wouldn't happen without isp support.
But a more ideal setup for this would be a load balancer. to split connections to ethier one to reduce load.