Final answer:
When canoeing upstream, it is advisable to stay near the shore to take advantage of the slower current due to friction. Conversely, when canoeing downstream, staying near the middle is ideal to benefit from the faster current in the river's center.
Step-by-step explanation:
When paddling a canoe upstream, it is wisest to travel as near to the shore as possible because the current is slower near the banks compared to the middle of the river. This is due to the friction between the water and the riverbed. By staying near the shore, you can take advantage of the slower current and expend less effort to move forward.
When canoeing downstream, it may be best to stay near the middle because the current is strongest in the middle of the river. As the river widens and deepens, the water in the middle has more space to flow, resulting in a faster current. By staying near the middle, you can harness the speed of the current and maximize your downstream progress.