When I use 'onstar', I give them a destination... the 'via' points and ask them "route me around metro areas and NO INTERSTATES... They are glad to help.
On my Garmin I can 'exclude' TOLL, interstates, etc.. I also have their map tool on my pc and can easily 'drag' lines around the nasty areas... a bit out of the way, but much less stress... Then I save the 'route' and download to the GPS..
Your experience will vary...
Peace and Blessings..