Use um construtor ARRAY :
SELECT ARRAY [bool_or(column_a)
, bool_or(column_b)
, bool_or(column_c)] AS arr_abc
FROM tbl
WHERE id IN (1,2);
SELECT ARRAY [bool_or(column_a)
, bool_or(column_b)
, bool_or(column_c)] AS arr_abc
FROM tbl
WHERE id IN (1,2);