CNY70 from 3.3v instead of 5v?
The CNY70 is just an IR LED and IR Phototransistor.  You can treat the IR LED (emitter) portion of it just like any LED and size the resistor appropriately. 

The receiver is just a phototransistor which can operate at anything from about 1V up to 32V with no need to adjust anything.  The resistor used there is merely a pullup resistor.  You can think of the receiver as a button. When enough IR light falls on it it turns "on".

On an Arduino you could even get away without the pullup resistor and use an input in INPUT_PULLUP mode.