Every fourth of July Canadians make the same mess as their neighbours (7)
I believe the answer is:
yankees
'neighbours' is the definition.
The definition and answer can be both people as well as being plural nouns.
Maybe there's a link between them I don't understand?
I don't understand how the remainder of the clue works.
(Other definitions for yankees that I've seen before include "multiple bets" , "Americans or northern states during civil war" , "Northern soldiers in the American Civil War" , "Code words on the radio for US" , "Side in US Civil War" .)