those are some mighty big black bears your describing :-? :-?!!
i'm sure less and less hunters apply for bear permits just  as in my state MI every generation is losing more and more hunters and fishermen??
i can relate to not finding the right combo of tree's but i wouldn't recomend hiding your food pack under a canoe :-/ :-/??
IF, you can't hang i would do what the "hiders" do, take pack away from camp and stash in woods. you could still do the pot and pan alarm thing or go to my "personal alarm" but i think you would be much better served keeping the canoe out of harm's way ;) ;)
it's BAD enough if a bear get's your food, but if he rips into your canoe to do it, well then your really screwed ;) ;)!!
if you go to link Azlea posted and study it out, you'll see that with using 2 top ropes, coming from opposite directions and using the pulley system closer to one tree or the  other, you SHOULD have better luck finding suitable tree's??
i bet when the word get's out about those big blacks bears, Pennsylvania will be a prime spot for the black bear hunter's??
from what i've read, you need to go to BC or some place farther north to get into bears that size??