Where is the largest amount of revenue come from for the NFL? TV revenue.
Buffalo, the team, yes could be worth more in Toronto, to the owner. Things that aren't collectively bargained, like suites, might sell more, therefore generating more revenue for the team.
The NFL is already in that market, they have TV deals with multiple Canadian cable providers. So that's revenue the NFL is already splitting up as part of the $6 billion it gets annually. Canada is also a bit weird with regards to TV deals, per the CRTC (Canada's FCC) no one provider can have exclusivity. So deals like DirecTV, you won't see in Canada, providers won't be fighting over each other to get those deals. So could the NFL get more money out Toronto team? Maybe, but IMO, it wouldn't be nearly as much as you seem to think. It's almost the same as a team moving to Los Angeles. The NFL already has people watching the NFL in LA, it's not like it's a black out in terms of NFL games, so moving a team there doesn't generate more TV revenue, which again is where the NFL makes most of it's money. In a lot of ways not having a team in LA is helping the NFL. If the NFL really truly needed that LA market for revenue, they would have a team there, I guarantee that.
Does it look good from a marketing perspective to have an international team? Sure. But the NFL is already in Toronto, making money, and making quite a bit.