I've never attempted to put a sail on a kayak, so I don't know that I
can help you much. Speaking as an avid sailor, I can tell you that it's
not a trivial problem. It's also not exactly rocket science. Try
googling on "Sailing Kayak" nad see what turns up.

Since I last posted, I met a guy who gets the wind to tow a canoe by
attaching a kite to the canoe using heavy (trolling - woven??) fishing
line. He claims that the canoe is much more stable than having a mast
that could cause the canoe to flip in a cross gust.

Has anyone else heard of this technique?