A motor and driver is rated as per phase, so if a motor is 4A, then get a driver that is rated at 4A or over.
To get any power that is useful from the motor you also need volts, so dont just look at the current.
As an example if you see a 10A driver that is only rated at say 30V, this will be completely useless for larger motors, unless you are happy watching paint dry.
In other words you may get the torque, but you wont get the speed.