You definitely can because the most basic version comes with the corolla motor.
But to answer your question as to why the difference, well, you have to remember the Celica came in different trims. Different trims = different motors.
They range from 1.8 liter motors to 2.2 liter motors
Curb weight of the vehicle also has a major part in mpgs as well.
And of course lets not forget maintenance of the car itself..