Just as a note of interest, I've been surprised to see that the Olympic water events featuring racers in what are obviously kayaks are being called canoeing.
Kayaking and canoeing (in English, German works differently) are nor only differentiated by the type of boat (open or closed) but also by the way to propel and steer them.
Kayaking is done with a double bladed paddel. Not all Kayaks are closed. For example sea water kayaks are often open with just some rests for the knees to balance the boat.
Canoeing is done with a single bladed paddel. While most canoes are open there are versions that are closed, especially for whitewater canoeing like the slalom at the olympics.
Also there are differences that are not immediately visible to the untrained eye like the presence of a keel, the position of the seat (front back middle), the ratio between length and width of the boat, even the way one sits inside is different.
Maybe think of it as the difference between table tennis and ping pong. The pro can go on about the number of huge differences... to me it's two people with miniature paddles, hitting little white balls towards each other.
Würde ein Sportvereins-Kajakfahrer sich eigentlich als "Kanuten" bezeichnen?
Ja. Immer. (Nur ganz wenige Ausnahmen, die zu stark vom englischen Sprachraum beinflusst sind, bilden die Ausnahme zur Regel.)
Unabhängig davon, ob man Cnadier, Kajak oder Drachenboot fährt.