Fitzpatrick went 21 of 38 for 217 yards with a 20-yard touchdown to Stevie Johnson. C.J. Spiller had 103 yards rushing and scored on a 14-yard run.
Wilson went 14 of 23 for 205 yards passing, and had 92 yards rushing.
It was an outing that came on an international stage on a day the NFL's two most talked about rookie quarterbacks were either hurt — Washington's Robert Griffin III — or lost — Indianapolis' Andrew Luck.
"The kid is destined to be great," receiver Golden Tate said. "You didn't expect Russell Wilson to even be in the Rookie of the Year talk. The fact that he's responded and led this team this far, I think that says a lot."
Running back Marshawn Lynch had 113 yards rushing and scored on a 13-yard run in his first game against his former team. Defensive end Chris Clemons had 2 1/2 of Seattle's three sacks.
The Bills dropped to 1-4 in regular-season games at Toronto since the series began in 2008.
The Bills and Toronto-based Rogers Communications are closing in on a deal to extend the series, which expired after this game.
Torontonians might want to reconsider after this. With 5:20 left, fans in one end zone began chanting "Let's Go Blue Jays!"
At least they were entertained by both the Seahawks and at halftime by Korean pop star PSY performed his hit "Gangnam Style" at midfield.
The announced crowd of 40,770 was well below the downtown domed Rogers Centre's capacity of 54,000. And many who stuck around for the second half started rooting for the Seahawks.
That was fine for Carroll, who made his first trip to Toronto.
"This was exciting for us. We looked at it like a little bit of a bowl-game situation," Carroll said. "The 12th man north was there."