By Rod Nickel (Reuters) – Horn-blaring demonstrations demanding an end to Canadian COVID-19 vaccine mandates for cross-border truck drivers have caused gridlock in the capital Ottawa since late January. The protests are now spilling to key Canada-United States border crossings and disrupting trade. Copycat protests have also sprung up in Australia, New Zealand and France, while truckers in the United States have said they are planning similar demonstrations. How did the protests start? COVID-19 vaccine mandates for cross-border truck drivers, imposed in January by Canada and the United States,…