When planning a bike route in unknown territory, the best thing to do is--in advance--ask people who bike there regularly; for example, on this forum.

No mapping website is going to be able to show you all the traffic/street conditions. Street View may or may not show you the traffic density you may encounter, as it's just a snapshot of whenever the Street View vehicle happened to be there; at best it can show you where roads are gated off or marked as private property (a clue being Street View omitting coverage of some section of a street where everything else around is covered).

The Google Maps folks have been quite responsive when I've reported problems with bike routes Google Maps has chosen. I strongly recommend you send them feedback. User contributions are a big part of improving Google Maps' biking directions.