San Marzano tomatoes differ from regular canned tomatoes in several ways. Firstly, San Marzano tomatoes are a specific variety that are grown in a specific region of Italy with volcanic soil. Secondly, they are renowned for their unique flavor profile, characterized by a balance of sweetness and acidity. Additionally, San Marzano tomatoes have a lower seed count and thick flesh, which contributes to their meatier texture and allows for a richer consistency in sauces.