Since add-on sail rigs usually allow you to play around with placement of the leeboards quite a bit, and since the typical canoe hull itself creates a fairly small amount of lateral resistance, you may or may not be able to get away with the mast stepped that far forward. The leeboards themselves are going to provide the majority of the boat's lateral plane and balancing the board position against the sail's area is going to be somewhat more important than where along the canoe's length the boards, mast and sail fall. That being said, stuffing the mast that far forward is seldom ideal from a performance and handling perspective. Canoes generally sail best with the leeboards under the sail's center of effort and pretty close to the center of the boat. This also gives the sailor the ability to easily use his weight to make changes in fore and aft trim, which in turn is a powerful fine-tuning tool for steering and helm balance.
As well as driving force, pressure on the sails creates a certain amount of downforce. If the sail is stepped way up in the bow it tends to give the bow stem a lot of "bite" which can make steering rather peculiar, the same way a paddling canoe which is bow-heavy can be squirrelly to steer. In most cases, boats which step their masts far up in the ends had more than one sail, balancing the sailplan fore-and-aft along the hull. You might find the main mast stepped through the deck, and a mizzen stepped through a thwart or seat somewhere in the aft half of the canoe. Other configurations were sailed stern first with the big mainsail stepped close to the leading end (stern seat or deck) and the mizzen stepped through the bow seat frame or the thwart right behind the bow seat. It would be fairly unusual to rig a single-masted boat with the mast that far forward if they were serious about the canoe actually sailing well. Stepping a single mast in the bow seat/bow quarter-thwart area usually works better as it places the center of the sail closer to the middle of the boat.
