Howard (5-0) remained undefeated through Draw 9 after beating Rob Rumfeldt of Guelph, Ont., 5-4 in eight ends. The Coldwater, Ont., native overcame an early 2-0 deficit against Rumfeldt (1-4) by scoring twice in the second and sixth ends.
McEwen improved to 4-1 after clobbering John Morris, who is skipping Kevin Martin's Edmonton rink, 7-1 in five ends. Morris dropped to 2-3.
The victory was McEwen's third straight of the day after earlier wins over Brent Pierce and Rob Fowler of Brandon, Man.
Meanwhile, Winnipeg's Jeff Stoughton (3-2) cruised past Jean-Michel Menard (1-4) of Gatineau, Que., 7-4.
Toronto's John Epping (1-4) scored two in the eighth end against Jim Cotter of Kelowna, B.C., to earn a 6-5 win, his first of the tournament. Toronto's Mark Kean (3-2) needed an extra end to beat Pierce (2-3), from New Westminster, B.C., 7-6.
Howard leads Pool A, McEwen holds Pool C and a logjam has developed in Pool B where Cotter, Brad Gushue of St. John's, N.L., Kevin Koe of Calgary and Jake Higgs of Harriston, Ont., are tied for the lead at 3-2.
The 18-team tournament is the second men's Grand Slam event of the World Curling Tour season and has a purse of $100,000.