If you go to the airline website (or even other booking sites) and click on details you can see the flight, operator, and the aircraft. In fact, some websites (

If you go to the airline website (or even other booking sites) and click on details you can see the flight, operator, and the aircraft. In fact, some websites (I think kayak) can even filter by including or excluding aircraft specific models. In worst cases, you might need to know the aircraft from the seat map. From my experience they rarely change what’s the aircraft, if they had it written, most likely it is the aircraft that you will fly with.