Connecting two spokes on two different subscriptions with 2 Azure firewalls on each side. See diagram:

References:

• https://learn.microsoft.com/en-us/azure/firewall/firewall-multi-hub-spoke#routing-on-the-spoke-subnets

• https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview#system-routes

• https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-outbound-connections

• https://learn.microsoft.com/en-us/azure/load-balancer/load-balancer-outbound-connections