The technology sector has been at the centre of a sharp recovery in US stocks since a market rout in February.
This earnings season has been stronger than analysts had expected.
The number of Americans filing for unemployment benefits unexpectedly fell last week, a Labor Department report showed.
The Toronto Stock Exchange's S&P/TSX fell 90.47 points, or 0.55 per cent, to 16,326.51, led lower by the health care, consumer staples and utilities sectors.
Mylan's 6.8 percent drop was the most on the benchmark S&P 500 after the drugmaker reported quarterly results and said it was actively evaluating a "wide range of alternatives".
The S&P 500 lost 7.07 points, or 0.2 per cent.
About 5.9 billion shares changed hands on US exchanges.
Investors will be looking at the index for clues about the Federal Reserve's latest monetary policy moves.
The Dow Jones Industrial Average on Wednesday was down 45.16 points, or 0.18 per cent, to 25,583.75.
The Dow is up 593.92 points, or 2.4 percent.
Seven of the 11 major S&P sectors were lower.
Chip stocks fell after Morgan Stanley downgraded the USA semiconductor industry, saying upside to estimates is hard to come by. Beijing announced Wednesday it would counter the most recent round of US tariffs with its own.
Shares of trade-sensitive companies declined, with Boeing, 3M and Caterpillar down between 2.3 percent and 4 percent.
The Nasdaq is up 935.72 points, or 13.6 percent.
Advancing issues outnumbered decliners by a 1.80-to-1 ratio on the NYSE.