Seafood soup is confined to British Quebec (6)
I believe the answer is:
bisque
'seafood soup' is the definition.
(soup made from shellfish)
'is confined to british quebec' is the wordplay.
'confined to' means one lot of letters goes inside another.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'quebec' becomes 'que' (abbreviation for Quebec).
'b'+'que'='bque'
'is' placed into 'bque' is 'BISQUE'.
(Other definitions for bisque that I've seen before include "golf handicap" , "Thick shellfish soup" , "Rich soup as made from lobster" , "Creamy soup" , "pot?" .)