You can’t easily force things like margins and orientation, all you can do is use

dlgPrint->PrinterSettings->DefaultPageSettings->Landscape = true;

Which if not forced and often ignored leaving the user to have to decide.

Detecting Page Orientation

You can do this in the print page callback:

	void DataGridViewPrint::PrintDoc_PrintPage(System::Object ^sender, System::Drawing::Printing::PrintPageEventArgs ^e)
	{
		if (e->PageSettings->Landscape)		//True for landscape