Metal container and flower containers in oil paintings (8)
I believe the answer is:
'oil paintings' is the definition.
(canvas is a kind of oil painting)
'metal container and flower containers' is the wordplay.
'metal container' becomes 'can' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'flower containers' becomes 'vases' (I've seen this in another clue).
'in' is the link.
(Other definitions for canvases that I've seen before include "Oil paintings, or pieces of cloth for them" , "Paint in oil on these." .)