I think you would still be able to choose your campsite, just as you do in the BWCAW.  It's just that you would not be able to camp on any site that was not designated as a campsite.  I can't imagine there being a problem finding unoccupied sites in Quetico, as there seems to be fewer paddlers in the park than ten or twenty years ago.  Obviously some areas would need more sites than other areas.

I'd rather not see "no-camping" signs in the backcountry.  People might just rip these down and camp there anyway.

My guess is that designated sites would be indicated by a fire ring and shown on park maps.  BWCA-type latrines aren't really needed except on the more heavily-used, easily accessed parts of the park, and I can't imagine that they would be installed anywhere in the interior in the foreseeable future.

The park currently encourages users to burn their toilet paper, as that stuff does not break down for years.  Burning TP should be a requirement.