I'm a US citizen and I wish to travel from Dallas to Toronto to Boston. I assume that I'll need my passport for this trip – Is this correct? And how much time (roughly) will it take to go through immigration and customs in Toronto and Boston?
Toronto Pearson has a website where you can fill in your flight details, and it will tell you if you need to cross immigration or not. https://www.torontopearson.com/Connecting.aspx
If it shows you have to cross immigration you will need a passport, otherwise not. In case you travel without a passport, you should be prepared to explain your connection at the gate in Dallas.