When purchasing a canoe or a kayak, it is essential to consider several factors that will guide you on the type of vessel to get. There is a great variety of elements, some subtle and others specific, but these are the basics:

Length
A general rule is that longer canoes achieve higher speeds through the water. Longer hulls also help to obtain a better track, holding a straight-line course and a bigger carrying capacity. On the other hand, shorter hulls are lighter in weight and more maneuverable.

Beam
The beam refers to how wide the boat is at its widest point. Wider canoes provide more room for cargo and stability. However, an increase in the beam causes the boat to move slower through the water. On the other hand, narrow beams are faster but have lower stability.

Depth
With all the other factors being constant, an increase in the depth of the canoe causes it to run drier in rough water. Greater depths also increase cargo space, but deeper canoes tend to be heavier and are easily pushed around by the wind.

Bottom shape
This has a lot to contribute to stability. The design can be flat; good for calm waters and beginners, round; easier to propel and high final stability, or vee. A compromise between round and flat with better all-around performance upon practice.

Sides. 
They can be flared; drier and more stable and harder to puddle, straight; compromise between tumblehome and flared with better dryness, stability, and ease of puddling, or tumblehome; not as dry or stable, thus requiring more skill.

Bow shape.
Bow-shaped, blunt and fuller shapes provide more buoyancy and shed splashes when on choppy waters and have more room for lightweight items. Thinner, finer bow shapes cut more easily through the water.

Rocker.
This is the fore and aft upward curve of the canoe keel line. Little rocker boats track better because more of the hull is down in the water, while more rocker allows the canoe to turn more easily.

Keel. 
External keels help the canoe achieve better track but catch on to obstacles. A good design of the hull offsets the need for an outer keel.