Fun fact: A lot of the 'Bushido' code as we know it, including the famous provisions on suicide-before-dishonor, was made up by the Imperial Japanese government at the turn of the 19th century. So many of the 'ancient traditions' which modern culture ascribes to the samuri were not, in fact, a codified thing they practiced.
However, the Code of Chivalry (dating back to Charlemagne) has provisions for honorable suicide. Knights just didn't really follow their honor codes very well, because they were extremely restrictive and tended to get you killed.
IMO Knights would win; plate armor > arrows, so long ranged combat would be out of the question and they'd have to close. Upon which point Shield > 2handing a katana (seriously, not having a means to parry or block other than with the blade is a bizarre trait for a warrior and only could have evolved in such an insular culture) followed by pretty much any weapon > lacquer armor.
Samuri did have a role they performed better in than a knight would, but that was as a highly mobile archer effective at suppressing light infantry or light cavalry. Seeing as that was all they were likely to face in their day, they were the most effective fighting force in Japan. If they were faced with anything else, they likely wouldn't have performed so well; their tactics and equipment just wasn't suited to any different role.