Showboat cancelled, commercial remains (3,1,4)
I believe the answer is:
cut a dash
'showboat' is the definition.
(to cut a dash is to dress in a showboating manner)
'cancelled commercial remains' is the wordplay.
'cancelled' becomes 'cut'.
'commercial' becomes 'ad' (abbreviation for advertisement).
'remains' becomes 'ash' (remains of a fire).
'cut'+'ad'+'ash'='CUT A DASH'
(Other definitions for cut a dash that I've seen before include "edit out hyphen" , "made a striking impression" , "To make a stylish impression" , "make a big impression" , "Behave or dress strikingly" .)