I got it to work. I turned off the WAN side of the Linksys and set it to be part of the LAN switch of the Linksys.
That's the beauty of running DD-WRT firmware on a Linksys. Changes a $50 router into a $500 one.
The WRT310N is running DHCP and I have the DHCP of the TG790 HF router turned off. The gateway for the WRT310N is pointing to 192.168.1.1. If you point it to 192.168.1.254, I can't get out to the internet.
I'm not keen on how these items are even working. An outdoor antenna that has a DHCP/DNS and a internal router that also has a DHCP/DNS. From the documentation I've looked over, it looks like the Cantenna is designed to work with multiple internal routers.
192.168.1.1 is the Cantenna. 192.168.1.254 is the HF router.
From what I can tell there is no way to change those values. Perhaps in the future there will be firmware/software upgrades to fix this.