Interesting question. The one in the stern is the only one that matters. The person in the bow provides some power especially when moving upstream. However, on placid waters a canoe has a maximum speed and all the power strokes in the world won't make it go any faster. The person in the stern can move a canoe by themselves and steer it with little assistance, if any. But he (or she) directs that assistance. Who sets the pace? It doesn't matter. The one in the stern is the one who sets direction and speed