300 amps (274 fla ) 3 phase 100' long going to a motor load with two parallel 2" rigid conduits

You should also tell us what kind of motor, the horsepower, starter across the line or frequency drive, AC or DC, single phase or three phase, and what the motor is connected to...

But given only the information you have provided, if three phase, #1/0 AWG copper keeps the voltage drop below 3%...

Be advised, if I knew all the above information I may recommend a different size...