The title isn't a huge mystery. Most of the book takes place in Cannery Row, so Cannery Row is a pretty safe choice for a name.
But—bear with us—what if the book were called Doc's Party (okay, that's pretty dumb) or Mack and the Boys? Then Steinbeck would be telling us that a certain character or group of characters is maybe more important than the others, and more important than the setting. By calling the book Cannery Row, Steinbeck's telling us that the place is more important than the characters.