Hauling a scooter or motorcycle on the back of a C has been discuses many times. Here are the problems
1. The See Saw Effect. Any weight behind the rear axle takes weight off of the front axle and that weight is transferred to the rear axle. And the farther back it is from the rear axle the more weight is transferred. I have seen the math formula on the forum that can tell you just how much but that is beyond my ciphering capacity. If your front axle does not have at least 70% of its rated load you will have handing problems.
2. The maximum weight load for most hitch receivers is at most 500 pounds
IMHO figure out how you can put the motorcycle on a trailer with your canoe.
