Winter Rye would work about as good as anything IMO. I've grown a variety called "Aroostook" that has its origins from your area, very hardy and produces a heavy crop that deer around here will dig through snow to feed on. Around here, that variety is a little higher priced, around $14.00 for a 56# bag. 50-60#s is about how much it would take to plant a 1/2 acre. Probably be best planted mid-August in your area, but I'm not sure of that.

Good idea to help those crab apple trees out. Along with cutting out the competing trees, I would spread a bag of lime around each tree. Something that has worked for me, is to use a spade to go as deep as I can, rock it back and forth to open a slit and then pour 10-10-10 or better yet, compost or well aged manure down in the slit and stomp it closed. Takes a little time, but that will bring a crab apple to the front.

You'll probably have to rely on luck with the bears LOL. I do know they will destroy just about any kind of fruit tree in short order.