Sunshine, we hear, giving boost (5)
I believe the answer is:
raise
'boost' is the definition.
(I know that boost is a more specific form of the action raise)
'sunshine we hear' is the wordplay.
'sunshine' becomes 'rays'.
'we hear' shows a homophone (sound like).
'rays' is a homophone of 'RAISE'.
'giving' is the link.
(Other definitions for raise that I've seen before include "Care for during childhood" , "Heighten" , "Inflate" , "Hoist" , "Increase; elevate" .)