RADISSON, Quebec — In February, the United States did something that it had not done in many years — the country sent more electricity to Canada than it received from its northern neighbor. Then, in March, U.S. electricity exports to Canada climbed even more, reaching their highest level since at least 2010.

The increasing flow of power north is part of a worrying trend for North America: Demand for energy is growing robustly everywhere, but the supply of power — in Canada’s case from giant hydroelectric dams — and the ability to get the energy to where it’s needed are increasingly under strain.

Many energy experts say Canadian hydroelectric plants, which have had to reduce electricity production because of a recent drop in…