The Americans extended their home unbeaten streak to 78 games (67-0-10). Canada has not defeated the U.S. since 2001.
Leroux, a Canadian-born U.S. citizen, broke the deadlock with a left-footed finish 3 yards out after a Becky Sauerbrunn pass got through two defenders and goalkeeper Erin McLeod inside the 6-yard box.
Hope Solo preserved the U.S. win in the 87th minute with a diving save of a Jonelle Filigno shot.
The U.S., ranked No. 1 in the world, also remains undefeated under second-year coach Tom Sermanni (14-0-3), and is a perfect 11-0 in Texas.
The 20,862 fans at FC Dallas' home stadium were the largest crowd since 2003.
The Americans outshot Canada 15-7, forcing McLeod to make four saves — but took more than 70 minutes to score against the seventh-ranked Canadians for the second straight meeting.
The win marks a strong start to a World Cup qualifying year for the Americans.
CONCACAF qualifying is at the end of the year, and the U.S. should be favourites to emerge out of the region.
Canada, the host for the 2015 World Cup, is the host and is automatically qualifies.
While the U.S. had the more dominant game, it was Canada that had the best chance of the scoreless opening half.
Moments after U.S. defender Whitney Engen had a goal disallowed for an offside call in the 39th minute, Canadian midfielder Josée Bélanger took possession and sent the ball through two American defenders to Diana Matheson.
Solo, who did not handle the ball in the first half, cut down the angle and Matheson's cross-body chip from about 6 yards trickled past the far post to preserve the scoreless half.
This came after a stretch where Canada picked up three yellow cards in nine minutes, as the Americans controlled possession after a sloppy first few minutes.
Engen's disallowed goal came off a spot kick after the third yellow card, that was headed about 12 yards, with Engen 6 yards offside as the defender buried a cross-body shot.
The U.S., which had been off since Nov. 10, continues play with two games against Russia on Feb. 8 in Boca Raton, Fla., and four days later in Atlanta.