Backing canvas held making bloomers (7)
I believe the answer is:
dahlias
'bloomers' is the definition.
(I've seen this before)
'backing canvas held' is the wordplay.
'backing' shows that the letters should be reversed in order.
'canvas' becomes 'sail' ('sail' can be a synonym of 'canvas').
'held' becomes 'had' ('have' can be a synonym of 'hold').
'sail'+'had'='sailhad'
'sailhad' in reverse letter order is 'DAHLIAS'.
'making' acts as a link.
(Other definitions for dahlias that I've seen before include "Herbaceous perennial plants of a Mexican genus" , "Tuberous Mexican flowers" , "'Hid, alas, among the flowers (7)'" , "Might Ali dash for the flowers?" , "bloomers" .)