OTTAWA — Canada’s retaliatory tariffs are set to take effect on Tuesday and with an American response almost inevitable, trade watchers are warning Canada should prepare itself for economic pain. “We may be in an escalating war, and the question is who’s going to have the greater threshold for pain in this, and are Canadians ready for it because it’s going to be painful,” said Fen Osler Hampson, professor of International Affairs at Carleton University. “I think it may be too early to go back to the table because the Americans will simply throw the same demands at us, and you know if...