If it is determined that it was an Iranian missile, Mr. Trudeau will have to grapple with the question of whether the United States, Canada’s most important ally, played a role in provoking the events that ultimately resulted in the loss of Canadians’ lives.

The plane crashed on Wednesday morning, only hours after Iran had launched a barrage of 22 missiles against two military bases housing American troops in Iraq. The Iranian attack was in retaliation for the United States killing of Maj. Gen. Qassim Suleimani, one of the most powerful figures in Iran’s leadership.

In a sign of the tricky diplomatic challenges that could lie ahead, reporters at a news conference in Ottawa on Thursday repeatedly grilled Mr. Trudeau as to whether the United States was partly responsible for what happened, by creating a volatile situation.