I don't think it's going to be as neutral as you guys think. Sure, it won't be like a crowd in Buffalo. But this is I think the 4th year they've played a game in Toronto. Talking to friends who live there (I'm in Toronto now, btw), the % of local fans that have taken the Bills on as their team has grown each year. The general consensus amongst fans here is that the team is destined to move here. It's just a matter of when, not if. It's a big city that thumbs it's nose down at Buffalo big time. That mindset helps with fans taking to the idea of the Bills being their home team.
It's still not going to be a big crazy overwhelming advantage. If the Hawks go up fast, whatever fans they have will be taken out of the game. But I don't think it will be neutral at all. The Hawks are popular in WESTERN Canada. BC and Alberta primarily. Back East the fans are all Patriots, Steelers, Cowboys, Giants, Packers fans, etc. They root for whatever teams have been popular and won titles. Canadian Seahawks fans out West are more likely to attend a game in Seattle than come out for this game.