Sea that upset a canoe (5)
I believe the answer is:
ocean
'sea' is the definition.
(I know that sea can be written as ocean)
'upset a canoe' is the wordplay.
'upset' is an anagram indicator.
'canoe' with letters rearranged gives 'OCEAN'.
'that' is the link.
(Other definitions for ocean that I've seen before include "tons of water" , "The deep" , "Large amount of water and" , "Huge body of water" , "A lot of water!" .)