The tact a lawyer is generally obliged to take is: advise the border guard that the information on the laptop is not controlled by the lawyer, and that the lawyer does not have the authority to give up the password.
A lawyer holds client information under the protection of solicitor-client privilege, and cannot be compelled even by court order to disclose that information, save exceptional circumstances (crossing a border not being one of those).
As a lawyer, the examples I keep in my back pocket if I am asked by a border guard to give up a password, after explaining the above, include: What if I represented a member of the border patrol in a potential dispute against their employer? Or a dispute between the border service and another branch of government? With my password, the border service could obtain access to communication that gives them an unfair edge, or perhaps inflames what would be an otherwise docile dispute. More importantly: would you or your colleagues, as border guards, seek the advice of and speak candidly with a lawyer about a potential dispute when you know that your employer might well be reading it?
Privilege lives high atop the field of concerns for lawyers, because anything that puts a chill on the communication with and advice of lawyers undermines the rule of law. Among other problems, not having rule of law puts a damper on the legal business, though it has historically been good for the hired-goons business.
The US and Canadian border guard in my experience steer respectfully clear of privilege.