(Adds strategists quote and details throughout; updates prices) * Loonie touches its highest since Sept. 7 at 1.2541 * Canada posts a trade surplus of C$1.9 billion in August * Price of U.S. oil settles 1.7% higher * Canadian 10-year yield hits a three-month high at 1.546% By Fergal Smith TORONTO, Oct 5 (Reuters) - The Canadian dollar strengthened to a four-week high against its U.S. counterpart on Tuesday as oil added to recent gains and data showed Canada"s trade surplus widening in August. The loonie was last at 1.2580 to the greenback, or 79.49 U.S. cents, after touching its strongest level since Sept. 7 at 1.2541. "Further oil price gains should continue to support the CAD," strategists at Action Economics said in a note. The price of oil, one of Canada"s major exports, climbed to its highest since 2014 after the OPEC+ decision on Monday to stick to planned output rises. U.S. crude prices settled 1.7% higher at $78.93 a barrel. Canada"s trade surplus widened to C$1.9 billion in August, easily beating analyst expectations, as strong exports of energy products outweighed a drop in two-way trade for motor vehicles and parts. Canada"s employment report is due on Friday, which could offer clues on the Bank of Canada policy outlook. Analysts expect the central bank to further cut its bond purchase program later this month. Gains for the loonie came even as the U.S. dollar edged back towards a one-year high versus major rivals. Canadian government bond yields were higher across a steeper curve, tracking the move in U.S. Treasuries. The 10-year touched its highest since May 25 at 1.546% before dipping to 1.536%, up 5.4 basis points on the day. (Reporting by Fergal Smith; Editing by Kirsten Donovan and Marguerita Choy)