Answer:
The volume of US trade with Japan is likely greater than US trade with Taiwan due to a number of factors, including the size of their respective economies, the level of economic development, and the presence of US businesses in Japan.
As for Canada being the US's best customer, there are several reasons for this. First, Canada is the US's closest neighbor and largest trading partner, and the two countries share a long history of economic and cultural ties. Additionally, Canada and the US have a number of agreements in place, such as the North American Free Trade Agreement (NAFTA), that promote trade and investment between the two countries. Furthermore, Canada has a highly developed economy and is home to many major US firms, which contributes to a significant level of trade between the two countries.