TORONTO, Sept 24 (Reuters) - The Canadian dollar weakened against its US counterpart on Thursday as the greenback notched broad-based gains and after domestic retail sales ​data failed to lift investor concern about Canada's economic outlook.The loonie ‌was trading 0.2% lower at 1.4125 per US dollar, or 70.80 US cents, after touching its weakest intraday level since July 14 at 1.4149."The loonie’s slide looks more like a ​rates-and-USD story than a sudden Canada-specific shock," said Tony Valent...