Dhaka, July 12 -- Canada will face a 35% tariff on exports to the United States starting August 1, President Donald Trump said Thursday in a letter to Prime Minister Mark Carney.It was the latest of more than 20 such letters issued by Trump since Monday, as he continues to pursue his trade war threats against dozens of economies.Canada and the US have been locked in trade negotiations in hopes of reaching a deal by July 21, but the latest threat appeared to have shifted that deadline. Both Canada and Mexico are trying to find ways to satisfy Trump so that the free trade deal uniting the three countries - known as the USMCA - can be put back on track."Throughout the current trade negotiations with the United States, the Canadian government h...