I've found that when Google sends you on a "bike path" it's very often possible to get a street view of said path where it crosses a road that has that imagery. Find the crossing point and put yourself in the center of the crossing and rotate the view. You'll be able to tell the quality of the bike path. More often than not, on my most recent tours, they've been ATV/snowmobile paths following abandoned rail lines. It's worth having some idea of their level of maintenance before committing oneself to following them for long stretches.