At the moment the print settings set to the WorksheetPageSetup class are not passed to the Print dialog which leads to bad user experience. If you set the print settings of the RadSpreadsheet like so:

WorksheetPageSetup pageSetup = this.radSpreadsheet.Workbook.ActiveWorksheet.WorksheetPageSetup;
pageSetup.PageOrientation = PageOrientation.Landscape;

and then select Print, the Spreadsheet print menu will show the print preview as landscape. However, when after that you click on Print for the default print dialog to appear and then click Preferences, you will notice that the preference is set to Portrait. The print job will be Landscape, but the incorrect information in the default dialog creates confusion.

This is an example of how to set the preference of the default dialog:

PrintDialog printDialog = new PrintDialog();
var printTicket = printDialog.PrintTicket;
printTicket.PageOrientation = System.Printing.PageOrientation.Landscape;