Cincinnati might be on the smaller end of NFL markets but it's not that small. About 2.2 million people in the Cincinnati tri-state area, Buffalo has about half that but was much larger in the 60's and 70's when our teams were founded. Still much larger than Green bay. Buffalo teams also get a large degree of support from expats and their children. I can run into Bills and Sabres fans almost anywhere I go. Even in Austin Texas I've gotten a "Lets go Buffalo" leaving the airport in a Sabres T-shirt. I know Sabres fans that have grown up in Ohio, Indiana, NYC, and even one that grew up in Edmonton (Also met some from southern Ontario that can't stand the LeafsNot throwing stones at either organization, but I find it remarkable that such a small city (Cincinnati) is able to support pro sports teams.
There use to be talk of bringing an NFL team to Toronto (GTA pop = 6+ million), but it has been all quiet on that front for several years now.
I'm sure there were factors (such as ticket price) but the Bills Toronto series is largely considered a huge failure (atleast on this side of the border). I hope you guys get a team someday but I don't think it'll be because a team doesn't have support where they are. It'll be because they can't extort the local government into building them a new stadium so they'll go somewhere that will. Serious question though, if you get an NFL team what happens to the Argos?