MOSFET source to drain Current
A MOSFET always consumes power from the circuit. It has no mechanism to convert energy from some other form to electrical energy. 

Therefore, the currents through a MOSFET always flow from a higher potential to a lower one. 

This means, for an n-channel FET, if the drain is biased higher than the source, current will flow from drain to source (through the channel). If the source is biased higher than the drain, current will flow from source to drain (through the body diode). 


  Now, Lets say I have connected Drain to higher than Source and current is flowing through the body diode, But at the same time I want to turn on the MOSFET Source to Drain channel to allow current to flow from the channel from source to drain parallel with body diode.


If you turn on the FET, you may get parallel conduction through the channel and body diode, but both currents will flow from drain to source, because the drain is at a higher potential.