Howard, from Coldwater, Ont., finished the tournament with an 8-1 record and won $24,000 in prize money.
"It's the best teams in the world, the best competition you'll play against all year, and we're comfortable here," Howard said. "You keeping plugging away and hope you make your last shot. Today we did that."
Howard has won two of the three Grand Slam events this season, winning the Masters in November.
Gushue, from St. John's, N.L., scored two in the seventh to tie the game 6-6 going into the eighth and final end. But Howard had the hammer in the eighth and won with a draw to the button with the last rock.
The final Grand Slam event of the season goes April 15-20 when Summerside, P.E.I. hosts the Players' Championship.