April 1 (Reuters) - Canada’s main stock index opened higher on Thursday, helped by gains in energy, mining stocks, while data showed the domestic manufacturing activity grew at its fastest pace on record in March. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 82.13 points, or 0.44%, at 18,782.8.