BEIJING — China intensified its punitive campaign against Canada over the arrest of a top Chinese technology executive by arresting a second Canadian working here and announcing on Thursday that both men faced charges of undermining China’s national security. China’s foreign ministry confirmed the second arrest, a day after suggesting that the first involved a comparatively mild administrative matter involving the registration of a nongovernmental organization. Accusing the two men of national security crimes — as yet unspecified — signaled a serious escalation of the diplomatic crisis. …Chrystia Freeland, Canada’s foreign minister, disclosed the second case, and during a news conference in Ottawa on Wednesday she urged China to let the legal process unfold. She also warned the administration of President Trump, too, not to further politicize what started as a legal matter involving accusations that Huawei had committed bank fraud.