The cheapest and smallest way of converting 3 V to 3.3 V
While the question does not specify the microcontroller under consideration, the popular 3.3V rated microcontrollers from Atmel, Texas Instruments and Microchip all tolerate supply rails down to 3 Volts, 2.7 Volts or in some cases even lower. 

Note also that a CR2032, or for that matter pretty much any battery, will drop in voltage as it depletes. Thus the constraint to be considered is not the nominal voltage of the battery, but the lowest voltage the battery can drop to and still be considered operational.

The microcontroller datasheet will mention what the absolute lower limit is.

The datasheet will also reveal whether some parameters of the microcontroller will behave differently under lower voltage. 

Many microcontroller families specify lower clock speed limits for lower supply voltages: Thus a microcontroller which is rated to operate on a 20 MHz clock at, say, 5 Volts, would be limited to no higher than perhaps 12 MHz at 3.3 Volts, and 10 MHz at 3 Volts.

Another potential point of difference would be any analog reference voltage output available from the microcontroller: Some microcontrollers offer a reference pin with output valid only as long as the supply rail voltage is sufficiently higher than the reference voltage.



In order to be able to operate a microcontroller even as the battery depletes, a simple 3-terminal boost regulator, such as the Holtek HT7733, is an option to consider:



This particular boost works down to 0.7 Volt battery voltage, and is very inexpensive (20 cents each in my part of the world). The circuit is simple enough to add to an existing design. It also does not require an external MOSFET, an advantage over the NCP1450.