Returns a Range object that represents the merged range containing the specified cell. If the specified cell isn't in a merged range, this property returns the specified cell. Read-only IXLSRange.

With Workbook.Sheets[1].Range['A3','A3'].MergeArea do begin
  Item[1,1].Value := inttostr(Rows.Count) + ' x ' + inttostr(Columns.Count);
end;