You must own the base game on Origin
Mass Effect 2: https://www.origin.com/usa/en-us/store/mass-effect/mass-effect-2/addon/mass-effect-2-dlc-bundle#store-page-section-description
Mass Effect 3: https://www.origin.com/usa/en-us/store/mass-effect/mass-effect-3/addon/mass-effect-3-dlc-bundle#store-page-section-description