The problem with the standard rack is not the weight of the canoe, approx 80 lbs?
The greatest force is exerted when an opposing vehicle in traffic passes in the opposite direction.
Read a semi at 70mph and you at 70 in opposing directions.
The upward pull of the canoe is tremendous.
You are liable if the canoe is released from your vehicle.
I would not trust a factory rack!!
Be sure it is fastened securekly to the gutter.