I haven't had google send me to an entirely unsuitable highway. It won't let me make a route which would be illegal. For instance, I can't plan a cycling route through the Lincoln Tunnel or on an Interstate Highway, because it's not legal to ride a bike in those places.

You can start with your friend's route, knowing it will be pleasant or safe or both, to varying degrees. That might be the maximum number of miles it will be, so you can estimate how long that will take. Or you can start the one Google cooked up. That should be quicker. It might not be as nice, since it's not hand picked.

Once you do one of these enough, you'll figure out how to modify it. But either is a decent starting place. In general, most roads where it's legal to cycle have a good shoulder if the speed limit is over 35 mph. At least that's been my observation in the NYC area, in NJ and NY.