In Washington on Wednesday, Prime Minister Stephen Harper and President Barack Obama will announce a landmark information-sharing agreement affecting the flow of goods and people between Canada and the United States.

The comprehensive new measures – including the logging and sharing data about travellers crossing the Canada-U.S. border – could have long ranging consequences for individuals, bilateral relations and the public purse.

Here are some key issues raised by the entry-exit aspects of the accord.

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What is an exit-entry control system?

It would overstate matters to say that the government has no idea whether you are coming or going. Mostly, it just has no idea if you are going. Neither Canada nor the U.S. systematically logs where, when and how people leave the country.

This is about to change. Promises to implement entry-exit controls along both sides of the Canada-U.S. border should give officials a more precise idea about who is inside -- and outside -- of North America at any given time.

Over time, such controls could develop into vast biometric databases. In North America and Europe, the development of such systems are raising questions about sovereignty and privacy.

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What are the advantages?

In Canada, the main hope is that increased confidence in cross-border security will facilitate bilateral trade. In the United States, the new measures help satisfy a recommendation by the U.S. 9/11 Commission -- that a "a biometric entry-exit screening system" be created to keep terrorists out of North America.

One likely spinoff benefit of these databases is that they could help governments crack down on cheats who reap benefits that they are not entitled to. This includes foreigners who overstay short-term visas; fraudsters who pretend to be meeting immigration residency requirements while actually living overseas; and the "jobless" who collect employment insurance while working abroad

Privacy watchdogs and civil-liberties groups, however, are wary of migration databases being mined for purposes other than that for which they were explicitly created.

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What are the disadvantages?

Experts say such systems are not an efficient way of red-flagging threats, given how they indiscriminately suck up information about the movements of the masses.

The databases themselves can also be enormously expensive to set up and run. Ex-diplomat Colin Robertson told the Canadian Press this week that implementing the data collection for the entry-exit system could cost Canadian taxpayers up to $1-billion.

And, as other federal security agencies are forced to cut back operations and personnel due to high deficits, Canada's border guards would likely need a significant top-up in resources. "We can't do it [exit controls]without more manpower, that's for sure," one Canada Border Services Agency official told The Globe.

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In the past, Canada's Auditor-General has pointed out how other federal security databases have become cost-overrun boondoggles (the gun registry) or chronically backlogged due to a lack of resources (RCMP crime databases).

What about privacy?

The Conservatives are pre-emptively playing down concerns. "The United States will not end up with more information than is already accessible," Deepak Obhrai, parliamentary secretary to the Minister of Foreign Affairs, said during this week's Question Period.

Yet Privacy Commissioner Jennifer Stoddart has repeatedly cautioned that if the two countries are going to marry their security systems, then everyone had better pay close attention to the "pre-nup." She recently wrote that if biometric data is "collected indiscriminately and stored in networked databases, we draw ever closer to the bleak reality of a 'surveillance society.' "

Right now there are many unanswered questions about how the entry-exit data of individual travellers would treated. How much will police get to tap into what are, migration databases? Will tax collectors get access? How far could U.S. agents reach into Canadian systems and vice versa? Will the data exist permanently? None of these details are clear at this time.