New Brunswick opponents of liquefied natural gas developments in Maine have given Prime Minister Stephen Harper a deadline to step in and stop the U.S. projects. Canada.com reported that John Craig, mayor of St. Andrews, N.B., said he's confident Harper will act to protect the pristine waters of Passamaquoddy Bay from environmental threats posed by proposed LNG terminals and tanker traffic. The town is giving Harper until April to clearly state whether tankers would be allowed to navigate Head Harbour Passage, an internal Canadian waterway, to deliver liquefied natural gas to terminals on the Maine coast. When that period expires - on April 7 - the town and opponents of the LNG proposals in New Brunswick and Maine will ratchet up pressure through letter-writing campaigns…