SQL cursor variable not working

My cursor variable @ProductNumber is not working if used in dynamic statement? 
It says "Must declare scalar variable". But this is a cursor variable. But when I used it not dynamic, it works. 
Please help.  Thanks.
DECLARE@TargetDB NVARCHAR(50)DECLARE@SourceDB NVARCHAR(50)DECLARE@DateEffectiveFrom datetimeDECLARE@InsertRecords NVARCHAR(1000)SET@TargetDB ='MySSISDb'SET@SourceDB ='MySSISDb2'SET@DateEffectiveFrom ='2013-12-29'Declare@ProductNumber INT;DECLARE@SqlDb NVARCHAR(Max)DECLARE Cur1 CURSORFORSELECT CAST(@SqlDb AS NVARCHAR(MAX))SET@SqlDb ='SELECT ProductNumber From '+@SourceDB+'.dbo.Item (NOLOCK)
             WHERE NOT EXISTS (SELECT 1 FROM '+@TargetDB+'.dbo.Item2 
                 WHERE ProductNumber   = '+@SourceDB+'.dbo.Item.ProductNumber)'EXEC sp_executesql @SqlDbOPEN Cur1FETCH NEXT FROM Cur1 INTO@ProductNumber;WHILE@@FETCH_STATUS =0BEGINSET@InsertRecords ='INSERT INTO '+@TargetDB +'.dbo.Item2(
                           ProductNumber,   ProductName, ListPrice, BirthDate) 
             SELECT ProductNumber, ProductName, 
                ListPrice, '''+CONVERT(nvarchar(25),@DateEffectiveFrom,120)+'''
         FROM '+@SourceDB +'.dbo.Item
         WHERE '+@SourceDB +'.dbo.Item.ProductNumber = @ProductNumber'--WHERE ' + @SourceDB + '.dbo.Item.ProductNumber = @ProductNumber --(this is where the     problem)EXEC sp_executesql @InsertRecordsFETCH NEXT FROM Cur1 INTO@ProductNumber;ENDCLOSE Cur1;DEALLOCATE Cur1;