@TPL23 Not sure why you'd want to use two physical routers? You should be using a router that allows for two+ WAN ports and can be configured so one of the ISPs is fail-over, or manage traffic to whichever one is faster and/or has less traffic and also will failover if one or the other is down. I have a whack of TP-Link switches, but they're all behind a Fortinet Fortigate which has fibre connections to two separate telcos who connect to different backbones (if one goes down, the other will be up).

With a single TP-Link router such as an Omada Gigabit VPN Router you can do exactly what you're asking and will have way fewer headaches and points of failure. I have no idea about TP-Link's firewall quality though as I have no firsthand experience with it. 

A single router with multiple WAN and load balancing is the better choice. If you're also concerned about being online should the router die, that's why you keep a spare router on hand (it can be identical and as expensive, or it can be a less powerful and less expensive backup). Using a single appliance allows you to be more on top of firmware updates and security bulletins, cuts the number of rules you have to set up to less than half, allows you to use DHCP without conflicts, gives you a single point for all your NATing and VLANs (etc.), and it reduces the ways into your network from the outside for you to lock down.