Tired and unhappy oarsman back in Canada (8)
I believe the answer is:
careworn
'tired and unhappy' is the definition.
'oarsman back in canada' is the wordplay.
'oarsman' becomes 'rower' ('rower' can be a synonym of 'oarsman').
'back' is a reversal indicator.
'in' is an insertion indicator.
'canada' becomes 'can' (common abbreviation eg in sporting competitions).
'rower' backwards is 'rewor'.
'rewor' placed into 'can' is 'CAREWORN'.
(Other definitions for careworn that I've seen before include "Haggard, drawn" , "Run down by anxiety" , "Tired through worry" , "worn-out" , "Showing signs of stress and worry" .)