By Soph Warnes, Elisabeth Buchwald, CNN (CNN) — For decades, the United States and Canada worked to build one of the world’s closest economic partnerships, with supply chains, businesses and trade increasingly intertwined. But now, with the two countries in the thick of a trade war, Canada is taking a dramatic step to reduce its reliance on the United States. It is forging closer economic ties with the European Union and is set to become its fir…