Plan to return by motorway to find seaside resort (5)
I believe the answer is:
miami
'seaside resort' is the definition.
(Miami is a resort city)
'plan to return by motorway' is the wordplay.
'plan' becomes 'aim' (aiming is a kind of planning).
'to return' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'motorway' becomes 'MI' (resembles Ma, English motorway).
'aim' in reverse letter order is 'mia'.
'mia'+'mi'='MIAMI'
'to find' acts as a link.
(Other definitions for miami that I've seen before include "Popular city in SE Florida" , "Popular sun-city of Florida" , "Resort city in SE Florida" , "Floridian city" , "Sunshine city in SE Florida" .)