SSIS always treat the Excel Source data as unicode. This is a issue which is very common when you are reading from Excel file. You have to read the data and then convert it to type(string, unicode) you desire to use. There are a lot of articles on internet which address this issue. You can find out on SQLServerCenteral.com or you can refer the below link.

SSIS: 3 Ways to resolve Unicode and non-unicode data type issue?