Derek Burney was Canada's ambassador to the U.S. from 1989-1993. Fen Osler Hampson is a distinguished fellow and director of Global Security at the Centre for International Governance Innovation and Chancellor's Professor at Carleton University.

Like any collision on a busy highway resulting from a fast-moving car veering without warning into the exit lane, Britain's departure from the European Union will trigger a multi-car pile-up that will be costly to all parties. It will generate uncertainty in Britain for investors, producers and politicians until new linkages are established, and it will add fuel to rising populism and nationalism that could lead to Europe's unravelling.

The verdict is not certain. Most polls suggest that the outcome of the referendum on June 23 is a toss-up. British Prime Minister David Cameron created an unnecessary crisis by promising a referendum and he will almost be history regardless of the result. He was not helped by U.S. President Barack Obama, who waded into Britain's debate with threats that the U.S. will not strike a separate trade deal with Britain if it decides to leave Europe.

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Most European leaders have wisely decided to hit the mute button about retaliatory measures.

Brexit explained: The latest updates and what you need to know

Mark Carney, who left the Bank of Canada to become Governor of the Bank of England, could also be a victim of Brexit. He has gone out on a political limb to warn Britons about the risks of a Leave vote, including the dangers of a "technical recession." Brexiteers who accuse him straying from his remit are livid. They have openly called for his resignation.

Brexit will also inflict collateral damage on Canada, though just how much is hard to predict. However, the Comprehensive Economic and Trade Agreement (CETA) between Canada and the European Union could be an early casualty. Europe is Canada's most important trading and investment partner after the United States. CETA is ambitious and far reaching. It promises to remove 98 per cent of European tariffs on Canadian goods while promoting closer ties on investment, government procurement, and regulation with the world's biggest market of 500 million people that has a combined GDP of $20-trillion.

The agreement was the result of years of painstaking negotiations. An agreement "in principle" was signed by the Conservatives in 2013. However, negotiations over some of the more contentious aspects of the agreement, notably its investment protection and dispute mechanisms, labored on. They concluded earlier this year with a series of amendments. Liberal Trade Minister Chrystia Freeland announced triumphantly that "Canadian investors and Canadian businesses will have their rights fully protected in this agreement." With characteristic optimism, she anticipated the deal would be ratified before the end of this year and come into force in 2017.

That may not happen if Britons vote for Brexit, for the simple reason that Britain has been Canada's staunchest ally during the CETA negotiations. It has done much of the heavy lifting to get its reluctant European partners to agree, for example, to the new provisions on investment. Europeans could use Britain's exit as an excuse to revisit negotiations or even put the agreement on the shelf. At the very least, ratification will be delayed as European governments struggle with far weightier matters of Britain's divorce.

As markets react to Brexit, the Canadian economy will also feel the shock waves. Canadian exports will be hurt by falling demand as Brexit further weakens what is already a sluggish European economy crippled by high unemployment and chronic recession. Canadian investors in Europe could also take a hit, especially those who do business in London, Europe's financial hub.

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There are secondary political effects of Brexit that should worry us too. Russia's Vladimir Putin would be the big beneficiary of a Leave vote. Sanctions regarding Ukraine would weaken, which would also affect Canada.

Brexit will also blow more wind into the sails of those, like American presidential contender Donald Trump, who want to fill the American moat with new tariffs and other protective measures. Brexit may also give oxygen to the dying embers of Quebec separatism, especially if Scotland, which strongly favours European membership, decides to file its own divorce papers against Britain.

Given the rising tide of protectionism in Europe and North America, the message for Canada is clear. We should move swiftly to improve our access in more promising Asian markets.