Use CStdioFile::WriteLine to generate a csv file, then launch the file in Excel with this:

Code:
::ShellExecute(m_hWnd, _T("open"), strFileName, NULL, NULL, SW_SHOW);
where strFileName is the name of the csv file. This will use the association of the csv extension with Excel to open the file in Excel.

This is a one way flow of data from your app to Excel. If you need anything more sophisticated, then Automation is your best bet.