So apparently, according to "I Hate Being A Philly Kid", Toronto is a small city. Do you mind if I list the cities with NFL teams that Toronto is larger than?
Let's start: Buffalo, Miami, New England (Boston), Baltimore, Cincinnati, Cleveland, Pittsburgh, Houston, Indianapolis, Jacksonville, Tennessee (Nashville), Denver, Kansas City, Oakland, San Diego, Dallas, Philadelphia, Washington D.C., Detroit, Green Bay, Minnesota (St. Paul-Minneapolis), Atlanta, Carolina (Charlotte), New Orleans, Tampa Bay (Tampa), Arizona (Phoenix), St. Louis, San Francisco, and Seattle.
Can you guess which cities are missing? Yes, New York and Chicago. Those are the only two cities that currently host an NFL team that are larger then Toronto. Now I know people are going to Wikipedia, looking at metropolitan population and taking it at face value. What we must remember though is that Canada does not define metropolitan areas the same way the US does. Dallas' population shows 6.4 million which is immensely higher then Toronto's 5.1 million but look closer. Dallas' metro area covers close to 5x the area. Miami, same thing. Phoenix, same thing. The Greater Toronto Area, when used in conventional speech, refers to more than just what the census says. Oshawa, for example is traditionally considered Toronto's western most suburb. It, like many cities, is not part of the Toronto metropolitan area according to the census. With those cities included, the Greater Toronto Area has a population of 5,600,000, good enough to rival cities such as Miami, Philadelphia, and Houston. Even then, more can be included. Hamilton, a city located 40 minutes drive from Toronto is not included in the Greater Toronto Area. With Hamilton and its suburbs included, the population of Toronto bloats to 6,500,000 which is larger than Dallas. Even then, it only covers roughly half the area Dallas does and that population creeps even higher when including the Kitchener-Waterloo region for example.
Now before someone complain that me including these are "not fair", take a deeper look. Miami includes Fort Lauderdale in its metropolitan area, Phoenix includes Tucson, Dallas includes Fort Worth. Toronto's population not only rivals, it surpasses all but 3 American cities. Now, I'm not going to sit here and pretend its close to Chicago, LA, and NY but it is larger then Dallas, Houston, Philly, and other American cities. So we've cleared that misconception up.
I'm not going to be given enough room to fully type out my answer and apparently they don't like me answering twice (probably to reduce the potential for spam), so I'll skim over the points. I've been over the population argument, so we'll leave it at that.
Corporate support is very important too and Toronto is very well set in that regard. It's the financial capital of Canada and is considered the 3rd or 4th largest corporate hub in North America (depending on where you place LA).
Stadium wise, the Skydome is likely too small at 55,000 seats and a new stadium would have to be built. This is extremely problematic because Canadian cities are traditionally much more dollar wise and don't like to spend on sports stadiums for private owners like American cities do. Toronto and the province of Ontario are especially bitter at this prospect. The Skydome went grossly over budget and was a total political nightmare at the time and neither are running surpluses right now in their budgets. A stadium could be built with a public/private split much like how BMO Field was built but on a grander scale I suppose.
Interest wise, its hard to gauge. Hockey is number 1 and nothing is ever going to chance that. The CFL's weakest market, believe it or not, is Toronto. However then you enter into a debate whether people are more interested in the NFL and that's why the CFL has been deemed irrelevant by many and what not. I don't really feel like arguing something that cannot be measured in anyway.
Lately? A Toronto group WAS in the bidding for the St. Louis Rams although they didn't get the team. The presumption was that they were going to relocate it to Toronto but there was no confirmation or denial for that matter on that. The group was unnamed but some names can be thrown around. David Tompson (Net Worth: $19 billion, See: Tompson-Reuters) was rumored at one point. MLSE is always considered interested however since the organization is owned by the OTPP, the NFL would not allow an ownership group of that size to own a team as it goes against league rules. Larry Tandenbaum has been in the news about it although he's not a billionaire and probably would need to team up with someone else. Maybe the RIM boys would be interested? At this point I'm just throwing out names but the point is Toronto has no shortage of billionaires who could own the team if interested.
I think I covered most things, sorry if I missed something.