Originally Posted by
seawolf
They can't because CBSA is performing background checks against Canadian law enforcement databases which CBP does not/nor should it have access to.
What makes you think CBP doesn't have access to Canadian databases, or the other way around? I believe there was a white paper some time ago that said they pull from US, Canadian, UK, and Interpol databases when someone pulls up or applies. Any information sharing agreements would almost certainly include those.