See this discussion under the Investigation section of the article on the air crash. The Chicago Convention governs who can claim access to the investigation and recovered remnants of the aircraft. The issues as to jurisdiction and claims to access have some complexities. The Ukraine has a right to access the investigation as it's a Ukrainian flagged airplane (by registration number) and carrier. The US NTSB has a right to access the investigation as the aircraft was made in the US (Boeing), and France's BEA (their equivalent to the NTSB) has a right to access as the aircraft engines were made in France. Under normal conditions this wouldn't be challenged, but seeing as Iran has primary jurisdiction over the crash site and aircraft remnants, I'd bet access by the US and Canada in particular (Canadian passport passengers) is highly unlikely. The more likely path of aircraft remnants access by the NTSB and Boeing is the Ukraine allowing access by the NTSB or Boeing once they're out of Iranian territory and jurisdiction. The details of who should have access and participation are explained in the Wiki article:
https://en.wikipedia.org/wiki/Ukraine_International_Airlines_Flight_752#Investigation
John
