North American tin commercial with actor McKellen (8)
I believe the answer is:
canadian
'north american' is the definition.
(Canadian is an example)
'tin commercial with actor mckellen' is the wordplay.
'tin' becomes 'can' (synonyms).
'commercial' becomes 'ad' (abbreviation for advertisement).
'with' says to put letters next to each other.
'actor mckellen' becomes 'ian' (I've seen this in another clue).
'can'+'ad'+'ian'='CANADIAN'
(Other definitions for canadian that I've seen before include "From the world's second largest country" , "from place across the Pond" , "One from Manitoba" , "Nationality of citizen of Vancouver" , "Can Diana be a strange North American?" .)