Desire to be under canvas? (6)
I believe the answer is:
intent
I believe this clue is a double definition.
'desire' is the first definition.
(thesaurus)
'under canvas?' is the second definition.
(I've seen this in other clues)
'to be' acts as a link.
(Other definitions for intent that I've seen before include "Design, aim" , "Meaning -- determined" , "Firm - plan - steadfast - purpose" , "Purpose; determined" , "'Purpose, aim (6)'" .)