April 30 (Reuters) - Canada’s main stock index opened lower on Friday after oil prices slipped on demand concerns, even as data showed the country’s economy likely grew by 0.9% in March from February, buoyed by strength in manufacturing, retail trade and finance. * At 09:31 a.m. ET (1331 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 91.19 points, or 0.47%, at 19,164.73. (Reporting by Devik Jain in Bengaluru; Editing by Shailesh Kuber)