jivefive,
The number is 4,800 TWh of power(550GWx8760 h ), NOT capacity, which is about 1100GW,(1.1TW) this is because NG capacity is x5 higher than production(22% capacity factor) and hydro (60%capacity factor) and coal(70%capacity factor).
The US only uses about half of capacity on average, Canada and Mexico higher amounts.

That's where the different numbers come in, Gail is showing capacity.

4,800 trillion watt-hours (4.8 petawatt-hours) of electricity used per year in the three countries. 1.1 trillion watts of capacity. Ok. Thanks.