Join one canal somewhere north of New York (11)
I believe the answer is:
connecticut
'somewhere north of new york' is the definition.
(Connecticut is north of New York)
'join one canal' is the wordplay.
'join' becomes 'connect' (synonyms).
'one' becomes 'i' (Roman numeral).
'canal' becomes 'cut' (cut is a kind of canal).
'connect'+'i'+'cut'='CONNECTICUT'
(Other definitions for connecticut that I've seen before include "America" , "Yale U. is in this US state" , "one of fifty" , "state of the union" , "The Nutmeg State" .)