The issue with your query is that the clause FROM c, UNNEST(...), UNNEST(...) is effectively computing the cross join between each row of c and the rows produced by each of the derived tables resulting from the UNNEST calls.
You can solve it by unnesting all your arrays in a single call to UNNEST , thus, producing a single derived table. When used in that manner, the UNNEST produces a table with one column for each array and one row for each element in the arrays. If the arrays have a different length, it will produce rows up to the number of elements in the largest array and fill in with NULL for the column of the smaller array.
To illustrate, for your case, this is what you want:
WITH data(a, b, c) AS (
VALUES
('a|b|c', '1|2|3', 'CAD'),
('d|e|f', '4|5|6', 'USD')
)
SELECT t.a, t.b, data.c
FROM data, UNNEST(split(a, '|'), split(b, '|')) t(a, b)
which produces:
a | b | c
---+---+-----
a | 1 | CAD
b | 2 | CAD
c | 3 | CAD
d | 4 | USD
e | 5 | USD
f | 6 | USD
(6 rows)