In the US, air travel made rail obsolete. For long distances (>500 miles) rail just can't compete with air. The was one of the main points in the book "Turbulent Skies: The History of Commercial Aviation" by T. A. Heppenheimer.
As for Boston to Toronto I have done it many times the past two years before giving driving a try so I know how much time it actually takes. Door to door it was within a half hour of total traveling time, ton cheaper, real food, and the security at the boarder was not stupid. Driving I can go there whenever I want without needing to plans weeks in advance, adding another last minute person isn't a $2000 plane ticket, and I can change my return home plans on a whim. And as a bonus when I rent a cars I have been able to try out different models which I personally very much enjoy.