Today I tried out my MOPAR roof rack and Canoe kit (from my Chrysler Pacifica) on my Jeep.
It fits (not perfect, but not bad - it will do)
Here are some pics I took of both items together.
If you buy the rack made for the GC it will no doubt fit exactly to the contour of the rails.
The canoe supports slide back and forth on the racks until it fits the canoe exactly, and tightens by the single bolt.
The supplied straps hook to the ring (see last pic).
But like I mentioned earlier, make sure the canoe doesn't go anywhere by using heavier straps at the front and rear of the canoe tied down to the vehicle.
I wish the rails were longer on the Jeep. They certainly could have extended further forward and back.
Mine are a homemade version of exactly that.