Canada is using a trade deal Donald Trump has threatened to scrap to formally challenge a U.S. decision to slap duties on softwood lumber. Foreign Minister Chrystia Freeland announced Tuesday the request for a dispute panel review under the North American Free Trade Agreement. The challenge is being led by government as well as several provinces and lumber companies including West Fraser Timber Co. and Canfor Corp. …Freeland, in a statement released by her office Tuesday, called the duties “unfair, unwarranted and deeply troubling” for Canadians, echoing previous statements on the lingering dispute. …The fifth round of Nafta talks begins Wednesday in Mexico City, and the Trump administration has already proposed eliminating the Chapter 19 dispute panels being used in this challenge from the agreement.