Can the US Custom force someone to unlock an encrypted drive or deny entry if you dont comply ? Im fine with the search but they have no right to scan my notebook etc.
The final decision of entry to a country(at that point) lies with the immigration officer. I imagine you can ask nicely for a review after you've been flown back to your point of origin.
I'll dig up some links, but seizure of non-citizen's computers at US borders is possible and scary. I treat the US border like a hackers conference - take a freshly imaged device, and refresh it on your return.