The pilot project was implemented following a diplomatic note between the two countries, and with administrative forbearance on some of the acts in place on both sides of the border. As to the carriage of firearms, the U.S. Coast Guard personnel were cross-designated under the RCMP Act as supernumerary constables. When they were operating on Canadian soil, they were operating under the direction and supervision of Canadian officers.
On May 7th, 2008. See this statement in context.