I use RideWithGPS to create my routes. I then send it to my Garmin Edge Explore. If I get off route it will not change the route but will try to direct me back to it, however if I ignore it and get beak on route at a later point it will pick it up and navigate from there. While off route depending on how far off I am and zoom level I can see the route on the screen.

I have also done this with a Garmin GPSMAP 64s and eTrix 20. You can also use the RideWithGPS phone app I think this is what I will do when my Garmin needs replacing.