You can go to FlightAware.com and enter your flight # which will give you a lot of data about that flight; below the flight map you'll see a log of scheduled flights and what aircraft will be used, plus a record of what aircraft were used in previous flights.
Some airlines' websites, e.g. JetBlue's, tell you the aircraft used for each flight when you go there to do your booking. I wouldn't say they're accurate 100% of the time but I think they generally are.
― Josefa, Wednesday, 9 December 2020 22:31 (three years ago) link