TORONTO, Aug 12 (Reuters) - Canada's main stock index was little changed on Tuesday as gains in financial and materials shares helped offset weakness in energy producers, with investors eyeing ongoing geopolitical tensions in Ukraine and Iraq. The Toronto Stock Exchange's S&P/TSX composite index was up 39.43 points, or 0.26 percent, at 15,301.07 shortly after the open. (Reporting by John Tilak Editing b W Simon)