I'm very sceptical of the devices ability to create a bike route on the roads that are on the map in the device. Garmin used to get their maps for road devices from NavTeq, which had technicians in the field checking conditions, additions to the data base, etc.... as well as developing routing that car units could recommend. That's changed a bit with the Google model to generate routing from the millions of smartphones it tracks and from which it generates routing. Bike computers can somewhat do that by using Strava's Heat Map or Garmins Popularity routing, which searches the data base of completed and uploaded rides. I have used the Garmin Return To Start function, which will give an option to retrace a recorded ride. Works very well the times I've played with it.

Would I let a device recommend a route otherwise ?, not likely as I don't think the devices are smart enough to make good choices and I KNOW that the bike option in Google cannot do this to my requirements,. Thus I (and most folks I assume) use the online systems of Garmin Connect, RQGPS, Strava, etc... to generate a route that is then downloaded to the device. It's feasible to develop a route if you have internet access (WiFi or cell data) via a smartphone (easier on a tablet, best yet on a computer) to use RWGPS (my choice) to trace a new route/course, then use the iQ connection to dump to the phone. The limit on a smartphone to trace a route is the accuracy of the finger press on a map. It's more accurate the larger the screen, IME. The Garmin Connect Mobile isn't terrible at course creation. Getting the route/course to the device is very easy in Garmin Connect Mobile or using the RWGPS iQ app.