HOUSTON :Oil prices were held in check on Thursday by threatened U.S. tariffs on Canadian and Mexican crude that could take effect this weekeend. Brent crude futures were up 27 cents at $76.85 a barrel at 11:05 a.m. CST (1705 GMT). U.S. crude futures were up 13 cents to $72.75. U.S. crude futures had settled at their lowest price this year on Wednesday. "We're getting close to the deadline and people are getting nervous," said Phil Flynn, senion analyst with Price Futures Group. U.S. President