Dual motor, but I don't think either one will do well towing a deer sled. The rear end would get so light that steering would be
very sketchy. A cargo trailer would be a much better option and an ATV would be best yet. (do they make electric ones yet?) Something like an ArielRider Grizzly. You'll have more weight over the front do to having the front hub motor, then if you loaded up a front rack to keep the front end weighed down, and pulled a trailer? Just remember that at that point, the rig is not really pedalable any more so if you ran the battery down you'd be pushing and it would be more work than just walking and pulling a sled or manual trailer.
Even on my Aventon Level.2 commuter bike, I raised the steering a bit and when I fully load the rear trunk and saddle bags, the steering is light and a bit wobbly at times. Got to spread the load, when it gets heavy.
If you got something like the Lectric XPeak (
LINK), and butchered the deer in the field so you could spread out the load, that might be doable, but I don't think that's legal. (I think you have to tag the complete deer and are only allowed to field dress the animal, right? So DNR can inspect if they want to)