Please don't use two motors. One big motor is better than two small ones
Well - that depends on what this "go cart" will be used for.
For instance, if you have two drive motors in the rear, you can (with appropriate feedback circuitry) create an electronic differential, as well as implement a traction control system.
This is more difficult to do with a single motor - if it driving a single wheel, forget it. If it is driving both rear wheels thru a differential, you will then need some means of monitoring wheel speed, slowing down one wheel or the other (some kind of ABS), and/or possibly being able to variably "lock" the differential. Even then, with all of that - you won't get the same kind of control you can have with two motors (on an automobile - like an AWD system - you are a bit stuck with the former system simply because a singular engine and transmission is involved - but if you had two transmissions from the engine - one for each wheel - then it could get interesting).