Never mind, I figured it out. I can place a '-updatecommand' hook on the createWindow, and then inside the handler I can test the WorldCanvas for 'ismapped'. As soon as it becomes mapped I can call viewAll on it.

sub updater {
   my ($i) = @_;
   #print "Updater called for canvas $i\n";
   if ($canvasViewed[$i] == 0 && $canvasList[$i]->ismapped) {
         $canvasViewed[$i] = 1;
         #print "trying viewAll for $i\n";
         $canvasList[$i]->viewAll;
      }
   }
}
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