The most effective place for a rudder on a sailing canoe is right at the stern. This puts it as far away as possible from the leeboard and rig and provides the best steering control. However with a canoe the best place for the sailor to be is in the centre of the canoe. This means that the canoe is trimmed neutrally, sitting level in the water when viewed from the side. It allows the canoe to be faster through the water as well as being more stable laterally.
With most sailing canoes, even with two people on board, it is better for both people to be seated near the centre, away from the ends. The central, widest part of the canoe provides more room for the sailor and crew to move towards the upwind side of the canoe when necessary, to counteract the overturning force of the sail. With a larger rig it is often necessary to get some of your weight outboard by sitting on the gunwale or any side deck.
All this causes a problem compared with a small dinghy with a transom where the sailor can sit nearer the stern and use a conventional rudder and tiller. In a sailing canoe the sailor will be half the length of the canoe away from the rudder, which could be over 8 feet, so the tiller controls need to be that long to reach the sailor.