Look at the drawings posted in the advertisement. The space needed for the clamps to attach to the cross member of your luggage rack (rails that cross over the top of the car--door to door) is 1 1/4 x 3 5/8. If your crossover rails are smaller than that then they can fit. You need cross-over rails for this to attach to not the side rails.
Yes. The attaching bolts are 4 inches apart on center, so it should fit, may be tight., But it will work
It does work for a canoe. I was reading the manual today and it actually states so :)
Yes.