NVARCHAR in SQLServer to VARCHAR in AWS Redshift
Got the answer from aws. 

NCHAR and NVARCHAR types are converted to CHAR and VARCHAR types, respectively, and are stored in the specified number of bytes. A VARCHAR(120) column consists of a maximum of 120 single-byte characters, 60 two-byte characters, 40 three-byte characters, or 30 four-byte characters.
So, if I am storing double-byte characaters in SQL using NVARCHAR(x), I can define VARCHAR(2x) in Redshift to have the same storage behavior.
Following is the link for further reference:
http://docs.aws.amazon.com/redshift/latest/dg/r_Character_types.html