The following example demonstrates how to call the Windows API function DeviceCapabilities(), to find out how a portrait page is rotated to achieve a landscape page, enabling you to adjust your output accordingly. Generally, a print driver will rotate a landscape page either 90 degrees, or 270 degrees from its portrait orientation. Example:

uses Printers;
{$IFDEF WIN32}
function DeviceCapabilitiesA(pDevice : PAnsiChar;
                             pPort : PAnsiChar;
                             fwCapability : Word;
                             pOutput : PAnsiChar;
                             DevMode : PDeviceModeA): Integer stdcall;
  external 'winspool.drv' name 'DeviceCapabilitiesA';
function DeviceCapabilitiesW(pDevice : PWideChar;
                             pPort : PWideChar;
                             fwCapability: Word;
                             pOutput: PWideChar;
                             DevMode: PDeviceModeW): Integer stdcall;
  external 'winspool.drv' name 'DeviceCapabilitiesW';
function DeviceCapabilities(pDevice : PChar;
                            pPort : PChar;
                            fwCapability : Word;
                            pOutput : PChar;
                            DevMode: PDeviceMode): Integer stdcall
  external 'winspool.drv' name 'DeviceCapabilitiesA';
{$ENDIF}
procedure TForm .Button Click(Sender: TObject);
var
  Device : array[0..255] of char;
  Driver : array[0..255] of char;
  Port   : array[0..255] of char;
  hDMode : THandle;
  Rotation : integer;
begin
  if PrintDialog .Execute then begin
   {Reset the printer}
    Printer.PrinterIndex := Printer.PrinterIndex;
    Printer.GetPrinter(Device, Driver, Port, hDMode);
    Rotation :=
      DeviceCapabilities(Device,
                         Port,
                         DC_ORIENTATION,
                         nil,
                         nil);
    case Rotation of
     0 :  ShowMessage('This device does not ' +
                      'support landscape');
     90 :  ShowMessage('This device rotates the portrait ' +
                      'orientation 90 degrees ' +
                      'to support landscape');
     270 :  ShowMessage('This device rotates the portrait ' +
                        'orientation 270 degrees ' +
                        'to support landscape');
    end;
  end;
end;