The key spec is the crystal's load capacitance requirement - multiply this by two to get the total capacitance for each end of the crystal, then subtract off the existing stray capacitance and the oscillator's own load capacitance.
Or just follow the guidance in the datasheet which says 18pF to 22pF capacitors (most crystals have a load capacitance of 10 to 18pF, if you provide a somewhat different value it will oscillate at a slightly different frequency.)
Most likely you will find that the tolerance on your capacitors is 10% or higher so your 20pF capacitor may actually be larger than 22pF and your 22pF capacitor may actually be less than 20 pF. So the bottom line is that it probably doesn't matter which value you use.