I can't think of any canoe rack setup better than the
Riverside Foam Blocks canoe rack kit. It is no where near as convenient as the canoe carrier systems made by Thule Racks and Yakima Racks, but if you are only occasionally hauling your canoe on the 07 Mercury Grand Marquis then the Riverside Foam Blocks canoe carrier kit will be fine. It's very inexpensive too compared to the Thule Rack and yakima Rack canoe carrier setups.