More than 100 China experts and former envoys to Beijing called on President Xi Jinping to release two Canadians who have been detained for six weeks, saying the cases undermine his efforts to build bridges to the rest of the world. The group, including former U.S. Ambassador Gary Locke, ex-Hong Kong Governor Christopher Patten and five former Canadian ambassadors to China, released an open letter to the Chinese leader Tuesday urging the two men’s freedom.