One in a canoe at sea where islands abound (7)
I believe the answer is:
oceania
'where islands abound' is the definition.
(region including many island nations)
'one in a canoe at sea' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'at sea' indicates anagramming the letters.
'a'+'canoe'='acanoe'
'acanoe' is an anagram of 'oceana'.
'i' going within 'oceana' is 'OCEANIA'.
(Other definitions for oceania that I've seen before include "part of the Pacific" , "Pacific group" , "Pacific Ocean area" , "Islands of the central and South Pacific" , "Polynesia, Micronesia and Melanesia" .)