In the end, the proper canoe paddle length is whatever is comfortable for you. Paddlers tend to collect different shaped and sized paddles for various situations, but the following guidelines are a good starting point:
While on land: Sit in a hard-seated chair. Sit up straight, and measure the distance from the seat surface between your legs, to your nose. This will be a good approximate length for the paddle shaft. Add to that length, the length of the blade of the paddle you are considering. Add 28" for our Merrimack paddles. Thus, if the measurement is 32", a 60" Merrimack paddle will probably be comfortable for you. Again, you may find that you prefer one a bit longer or a bit shorter. For our Whiskeyjack paddles, add 24".
While on water: Sit inside your canoe and measure the approximate vertical distance from your nose to the waterline. This measurement should match the distance from a paddle's grip to the top of its blade. Then add the length of the blade to get the correct overall length for your paddle.
As you become more experienced, you might develop a preference for a longer or shorter paddle, depending on your style of paddling and the type of canoe you have.