I found this on secondary customs screening at the ezbordercrossing website

[HereSince1628]

http://www.ezbordercrossing.com/the-inspection-experience/what-they-know-about-you/

I can't speak to the credibility or the politics/business interests of that site. There is a suggestion that records of interactions with police...as could occur in response to report of a suicide or attempt...rather than health records are searched.

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If you are pulled over for a secondary inspection or search even more information is collected and put into the database. This includes the reason for the additional screening, the results of the search, interview notes, details of any action taken, and the names of your travel companions.

Below are some of the things the U.S. and Canadian Border Patrol may be able to see if you are pulled in for a secondary inspection:

Criminal history. This may also include health records that involve contact with with the police – such as suicide attempts
Family members and relatives
Delinquent Tax status
Current Job
History of when/where/what times you have crossed borders – including state ports where there are border checks

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Obtaining a Copy of Your File Information

Both the U.S. and Canada have a way for you to obtain a copy of the information that the government has collected about you. To get your information from the U.S. see our page on the Freedom of Information Act. To ask Canada for your files see our page on the Privacy Act. Given that the two countries are swapping information, it is possible that parts of your files from both countries could in in the records you receive. However, getting this information is not as easy as it sounds so expect it to take some time and energy