Load-balancing Internet connection with docker on RPI

I wasn’t sure on how to explain my situation. so I drew this diagram.

basically I have more than one ISP and I would like to use docker on my Raspberry Pi to Load-balance my internet connection. inside an ISOLATED container. and then tell RPI to use that container as it’s default gateway.

for Load-balancing part I am using Net-ISP-Balance with resin/rpi-raspbian as the base image.

in my current approach docker uses --net=host. so changes that are applied to routing tables are permanent (until reboot). even though the container is down. (that’s expected of course because of --net=host but I am trying to avoid this)

so in an isolated container, if anything goes wrong I can immediately use my default gateway without reboot or flushing my tables.

I’m new to docker and I haven’t played with networking aspects of it. so I need help on creating these bridges and presenting the container to RPI as it’s default gateway