Reuters: Strains over stalled Canadian oil pipeline projects and Ottawa's push to impose a national carbon price hung over talks on Thursday between Prime Minister Justin Trudeau and the country's 10 provinces on how to tackle global warming. Trudeau's Liberal Party won an election last October on a pledge to do much more than the previous administration to curb emissions of greenhouse gases, which are climbing as firms exploit Canada's vast crude-rich oil sands. Behind the scenes, Trudeau officials have...