OTTAWA — Canada is turning to the North American Free Trade Agreement in its bid to stop U.S. duties on Canadian softwood lumber. A letter from a Canadian lawyer was hand-delivered Tuesday to the American NAFTA secretariat in Washington, requesting a panel review “in regard to the final determination of the U.S. Department of Commerce in the countervailing duty investigation of softwood lumber from Canada.” …Natural Resources Minister Jim Carr has repeatedly said Canada has every reason to believe it would prevail in such a challenge again. …However, until Tuesday it wasn’t clear whether Canada would take that route again in the midst of difficult NAFTA renegotiations, particularly given the American objective to eliminate Chapter 19 altogether.