SYDNEY, July 26 (Reuters) – Asian markets were trading mostly weaker on Wednesday ahead of the U.S. Federal Reserve's expected interest rate rise to be delivered later in the day, as investors also weighed the likelihood of a Chinese economic stimulus package. MSCI's broadest index of Asia-Pacific shares outside Japan (.MIAPJ0000PUS) was flat, after U.S. stocks ended the previous session with mild gains. The index is up 3.8% so far this month. The yield on benchmark 10-year Treasury notes rose to 3.8924%, compared with its U.S. close of 3.912% on Tuesday. The two-year yield , which rises with traders' expectations…