Solution: http://sqlblog.com/blogs/andy_leonard/archive/2007/07/22/ssis-design-pattern-dynamic-sql.aspx

SSIS Expressions Using nest Double Quotes

The best way I've found to do this is to write the query as I'd like it to appear, then copy it and paste it into notepad. I then replace all the quotation marks (") with slash and quotation marks (\"). (EXCEPT for the FIRST & LAST Quotation Marks)

If you then copy this and paste it into the expression builder, you merely need to nest it inside opening and closing quotation marks.

EXAMPLE:

This:

@[User::Excel2007Files] + "\\XLS_Test_Type_T.xlsx;Provider=Microsoft.ACE.OLEDB.12.0;Extended Properties="Excel 12.0;HDR=YES";"

WOULD BE CHANGED to THIS:

@[User::Excel2007Files] + "\\XLS_Test_Type_T.xlsx;Provider=Microsoft.ACE.OLEDB.12.0;Extended Properties=\"Excel 12.0;HDR=YES\";"