First of all ... yes, you're right, there are already folding canoes. Those boats don't necessarily pack up all that small, though, and typically weigh in the neighborhood of at least 18 kilograms (40 lbs). They're portable, but you'd certainly notice that you were carrying one. Israeli designer Ori Levin, however, has created a one-of-a-kind folding canoe called the Adhoc, that tips (no pun intended) the scales at just 4.1 kilograms, or 9 pounds.
The single-passenger Adhoc features a carbon fiber frame, and a hull made from aramid fabric, which is also used in racing sails. Custom-made locking mechanisms hold the telescoping longitudinal framework poles in place at the bow and stern, while a "parasol-like" center folding mechanism allows the boat to hold its shape in the middle. Its single seat is a hammock-like fabric and webbing arrangement.
The whole canoe can reportedly be stowed in a bag the size of a regular backpack, and assembled within about five minutes.
While there's no word on how stable or hydrodynamic the Adhoc is, as you can see below, it does at least float with a passenger aboard.
Needless to say, such a craft is probably not intended to replace anyone's traditional canoe. As something for hikers or forestry workers to carry along just in case they need it, however, it could conceivably be a viable product. That said, there is currently no word of the Adhoc being commercially produced.
If rowing is more your style, you might also be interested in reading about the Foldaboat.
The video below illustrates how the Adhoc fits together.