The torque of the motors is somewhat important, as it will reduce the slow-down of the flywheels when they grab the can. If the flywheels are heavy enough, then the motor torque doesn't matter much, other than determine how quickly you can adjust the speed.
Any motor that can get to 6000 rpm will work fine, as almost all motors work well at rpms below their maximum. You can control the speed using PWM if you have the appropriate controller circuit and H-bridge driver for the motor(s). Or, if the motors ever only rotate one way, all you need is a power MOSFET that you can drive with PWM.
Finally, you need an encoder to figure out how fast the motor is spinning, so you can adjust the PWM duty cycle to affect the speed. Some motors have built-in encoders; other systems put the encoders on the output (such as on the flywheels.)