Are there purpose built racing sailing canoes?
Progressively more and more so. Some have even become very hi-tech with the inclusion of modern sail clothes of Mylar and aluminum masts in order to reduce the weight and make rigging somewhat easier. They are constructed somewhat more robust in order to accommodate the weight of the rig and to withstand the additional strain created by the stresses that are created by sail power. Some are built to a shorter length for only 4 crew rather than 6.