You're way wrong about that. Toronto has been trying to get an NFL team for decades. Most of my Toronto friends are diehard NFL fans.
The Bills are playing in Toronto today, actually. And they'll be playing 8 games over the next 5 years in Toronto, including regular season games.
Regarding the capacity of the new Pens arena:
They may be popular now, and the NHL may be on a slight rise in popularity, but eventually there will be a dip/decline in popularity and/or greatness of the Pens. It looks a lot better to have a 19,000 seat stadium with, let's say, 500 empty seats, than to have a 25,000 seat stadium with 10,000 empty seats.
Just ask the Lightning when they played in the Thunderdome, which had a capacity of 26,000 for hockey, and was nearly empty most of the time. It looked awful.