The French put up close to Canterbury, a cathedral city (3)
I believe the answer is:
ely
'a cathedral city' is the definition.
(I've seen this before)
'the french put up close to canterbury' is the wordplay.
'the french' becomes 'le'.
'put up' says the letters should be written backwards.
'close to' suggests the final letters (the close/ending of).
The final letter of 'canterbury' is 'y'.
'le' reversed gives 'el'.
'el'+'y'='ELY'
(Other definitions for ely that I've seen before include "'Isle' in Cambridgeshire" , "Cambs diocese" , "Cambs. city" , "East Anglian city" , "English cathedral city" .)