Now that you know about the available materials, you need to decide what you plan to do with your canoe. Understand up front, there is not a perfect design for all conditions. You will not take a 17-1/2 foot long touring canoe into Class IV water. Likewise, you will not take a 14' canoe on a week long backcountry trip with three people. If you plan to do multiple activities you need to resign yourself to the fact that you will have to probably buy more than one canoe. Most avid paddlers own several canoes that they use for specific purposes.
Length: Because a canoe is a displacement hull, the longer it is, the faster it's theoretical top speed is. Most of us will never paddle hard enough to reach that "on paper" top speed of course and the Coleman Scanoe™ breaks that rule by getting the canoe up on a plane. The longer a canoe is, the more weight it can carry. Touring canoes are ideally 16 to 18 feet long and easily accommodate two people and a weeks worth of gear. They can also easily accommodate a family of four and a weekend worth of equipment.
The longer a canoe is the more difficult it is to control, especially if you are solo. A 17 foot long touring canoe can be a beast for a solo paddler on a windy day. As it is with larger canoes, the longer they are, the harder they become to steer. If you are paddling on a difficult course with a fast current (which due to terrain could still be considered Class I or Class II-) you may have a very challenging time. This is especially true of mid-western rivers. On flat water however, a long canoe is a pleasure as the length of the hull allows the canoe to track straight, and does not require as many corrections.
Shorter canoes are much easier to maneuver, and are better suited for solo paddlers. Canoes can be as short as 10' and are good for short jaunts, day trips, and whitewater adventures. Much easier to steer, shorter canoes typically don't track as well, and require a lot of correction to keep on a straight course in flat water. A novice paddler can find themselves zigzagging across a lake in frustration.
A good length for a general purpose canoe is 14 to 15 feet. This canoe will easily accommodate two people, but can be paddled solo. It can be taken into whitewater, but could be pressed into a weekend trip. It also has a good balance of maneuverability and straight line performance.
10 to 13 feet: Good solo canoe length, great for moving water, easy to maneuver, does not track well (straight line), limited capacity
14 to 15 feet: Good overall canoe length. Good for moving water and still, can accommodate a solo paddler or tandem crew, good at maneuvering and straight line tracking, capacity for weekend trip or third passenger
16 to 18 feet: Good touring canoe length. Not recommended for water above Class II+ or solo paddling, excellent straight line tracking, fair at maneuvering, capacity to handle a lot of gear and multiple passengers.
In excess of 18 feet: Sometimes called war canoes, typically require more than two paddlers and specific training to use. Great for groups with heavy loads. Very difficult to maneuver, and next to impossible for a solo paddler, large group can have excellent straight line stability and may even have the person in the stern seat work a rudder or use a paddle as one
Stability: Canoe stability is typically described in sales literature in two categories, initial stability, and secondary or final stability. Canoes that have good initial stability will not have good secondary stability and vice versa. A canoe with high initial stability will feel stable when stationary and flat in the water. However, lean to far out to paddle, and you will quickly find out that your canoe has low secondary stability and will feel very instable. A canoe with low initial stability will not feel as settled when stationary, and can be rather unsettling when you first climb in. However when you go to paddle and the canoe leans you will quickly learn that it resists the urge to tip over much better.
High initial stability is usual characteristic of a flat hull. As you lean over and the canoe rolls, there is nothing to "bite" into the water to keep the canoe from capsizing, this is why as you paddle they can feel very instable.
High secondary stability is usually the characteristic of a rounded or "v"