One of the ways I have used Google Maps for route planning is to zoom to the area in question, and grab the small person icon that you use to convert to street view. However, don't drop the icon on a street, just "hover it" over the entire area. All the places where street view is available will turn blue. These roads are generally paved. There may be exceptions, but so far this has worked very well for me through a number of places to include Minnesota, North Dakota, and Montana. I then spot check rather than doing an entire street view. When a paved road turns to gravel, the blue shading ends.

I did ride a road this year that was shown as paved on Google Maps and even the street view, but when we got there, the road ran right into a brand new lake. Google Maps, like printed maps, takes time to be updated. And of course there are periodic errors. I often compare Google Map data with state road maps and state bicycling maps, when available.