FWIW It may be better to mount the transducer toward the front of the canoe so that you see where you are going and not where you have been. In a practical sense I'm not sure this is actually accomplished considering the short time delay between data gathering and display but if the transducer is mounted in the back you will definitely be looking at what you have already passed over.
It would be wary of mounting the ducer both too far forward and right on the centerline, in other words the thickest parts of the hull. There is too much possibility of a stray bubble in the resin. Bubbles in the resin of the hull or the silicone or whatever the ducer shoots through must be avoided to get good results. Most successful mountings I've seen are under the bow seat.