Says they're south of Canada? (6)
I believe the answer is:
states
'says' is the definition.
('state' can be a synonym of 'say')
'they're south of canada?' is the wordplay.
'they're' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'south of' says to put letters next to each other.
'canada?' becomes 'state' (canada is a kind of state).
's' after 'state' is 'STATES'.
Can you help me to learn more?
(Other definitions for states that I've seen before include "Sets out; lands" , "Conditions of American administrative units" , "They're united in America" , "they may follow United" , "Governments" .)