Canoe in the bed of the truck, angled with the back to the inside passenger side out the back so it does not stick out in traffic, with the tailgate down and a red flag on it if it extends past 3 ft. It is not he best solution, and it will break down the canoe in the hinge point if done too much. Fill the bed portion with coolers and stuff to keep weight in it to keep from bouncing. Tie it in good at the cab and at both points where it sits on the tailgate.
I did this method many years when I owned a pickup, it served me fine. Be careful when you cross dips and make sure you don't drag the back off. If you are expecting a trip with a lot of rain, turn it upside down and transport the same way.
Racks, carriers, trailers are all better options. But the canoe can be carried this way too.