I use several methods of routing, and in order of preference
www.bikeroutetoaster.com Needs some setting up but worth it.
Start at the editor tab, and for 1st use you'll need to drag editing, summary and routing to top left window (4way arrow to move near title) this leaves help/elevation and cue sheet to go together, then drag map side and bottom bars down to make map as big as possible (elevation and help are therfore big too - handy).
On routing tab tick 'auto routing' and choose 'bicycle' and drag bike path slider to whatever rating you fancy.
On map tab in upper right corner is a map choice drop down - choose open cycle map to see all cycle routes superimposed (these are 'crowd sourced' GPS plotted maps, but the paths are manually input so are occasionally a bit wrong).
Then at top of map is 'go to' - type in start place and map zooms there, left click actual start point then at as many points as you like towards the end, this allows you to review proposed route as you go and pick preferred options. If you click start point and direct to the end you'll probably find some sections you'd rather change so it's easier as you go.
Once happy with the route then export as a tcx file, this format blindly follows your chosen plot without the GPS trying to 2nd guess and re-route as it sees fit.
Or
www.cycle.travel will do a great job from the off as it is cycle friendly, I prefer look of bikeroutetoaster map is only difference.
Or use
www.gpsies.com and search for a previously ridden route either by place name or map view, select road bike/mtb/cycle as suits your steed and filter in/out distances and climb and see whats available.
Or give a landmark at each end and await suggestions!