A 3" MAF tube will be fine for up to about 12psi on the 2.0 duratec, after that you'll basically be at the voltage peak and need a MAFia. Of course that is 12psi with my setup, not necessarily yours. It will be up to you to log the MAF voltage and determine if you need a MAFia.
'06 forged, GT3082R turbocharged, meth-fed Focus. 12.43 @ 115