To take a rest this way can look hard! (5)
I believe the answer is:
stare
'look hard' is the definition.
(I've seen this in another clue)
'to take a rest this way' is the wordplay.
'to take' means one lot of letters goes inside another (inserted letters are taken in).
'this way' indicates anagramming the letters (another way of arranging the letters).
'rest' anagrammed gives 'stre'.
'a' inserted into 'stre' is 'STARE'.
'can' is the link.
(Other definitions for stare that I've seen before include "Look with fixed eyes" , "Gawp" , "bird" , "Look hard" , "Long fixed look" .)