Final answer:
The magnitude of the velocity of the canoe relative to the river is determined by the difference between the speed of the canoe and the speed of the river.
Step-by-step explanation:
When considering the magnitude of the velocity of a canoe relative to the river, we need to understand that the resulting velocity is the vector sum of the individual velocities of the canoe and the river.
In this case, the magnitude of the canoe's velocity relative to the river would be the difference between the speed of the canoe and the speed of the river. Mathematically, we can calculate this by subtracting the speed of the river from the speed of the canoe.
Therefore, the magnitude of the velocity of the canoe relative to the river would be the difference between the speed of the canoe and the speed of the river.