Hello,
I can help you on this project, I have done it many times before, I do manage data centers that runs many failover situations. What you need to do is to add three floating static default routes and have them all tracked so those gets enabled/disabled based on your preferences. Please send me an email if you like to discuss the details, I can be contacted at jrochasolis at gmail.
If you're running bgp on at least two of the circuits, you can do the failover via prepends on bgp.
Thanks,
Jorge Rocha