OP - In my limited experience I've found that while the bicycle option on Google Maps is a decent place to start, but it omits alot of good bicycling routes. For instance, there is an excellent 10-ish mile long country road loop here in my hometown that almost no one ever travels, has great visibility, and therefore it makes a great training venue, but its not shown on Google Maps as a bike route. I'm not sure what criteria they use to select which routes are considered good for bikes, but I suspect it might be the presence or absence of wide shoulders, dedicated bike lanes, etc. The road I mention has neither. I would recommend that you also look at other resources like Strava Global Heatmap (which visually shows you real data from anywhere in the world you are interested in what routes are preferred and used by cyclists the most).

Keith