U.S. railway operator Kansas City Southern KSU.N said that it had accepted Canadian National Railway Co's CNR.TO $33.6 billion acquisition offer, upending a $29 billion deal with its competitor Canadian Pacific Railway Ltd CP.TO. May 14 (Reuters) - Futures for Canada's main stock index rose on Friday, as gold prices gained on a weaker U.S. dollar after U.S. Federal Reserve officials downplayed inflation concerns. The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE ended 0.15% higher at 19,135.81 on Thursday.