As the United States and China began talks Thursday to resolve a huge trade imbalance and avert tariffs that would hurt both countries, the Maine International Trade Center prepared for its annual meeting Friday that will focus on accessing Asian markets. The two economic superpowers are negotiating to cut the $375 billion trade imbalance — the difference between what the United States exports to China and what it imports — by $200 billion by having China buy more American agriculture, semiconductor and natural gas products. Despite the discord, Maine companies are growing throughout Asia, with the region being the state’s second-largest export partner after Canada.