The criteria used to turn over the names are secret, as is the process itself.
But a new cache of WikiLeaks documents pertaining to Canada lays bare the practice. It contains not only frank assessments by U.S. officials of Canadian co-operation, but the names of 27 Canadian citizens turned over by their own government as possible threats, along with 14 other names of foreign nationals living in Canada.
In at least some cases, the people in the cables appear to have been named as potential terrorists solely based on their associations with other suspects, rather than any actions or hard evidence.
Of the 41 people named, 21 do not appear to have ever been charged, and some had never come to the attention of the Americans before being named by their own government. Most of the remaining 20 names comprise the group known as the Toronto 18. Some of that group were charged and convicted; others had charges against them stayed.
The cables are a snapshot of periods in 2009 and 2010. Over the years, the number of names handed over is certainly much higher.
The first stop for these names is usually the so-called Visa Viper list maintained by the U.S. government. Anyone who makes that list is unlikely to be admitted to the States. (read more)