What is the plural of "scenario"?

What is the plural of "scenario"? I have always used "scenarios", but have recently come across "scenaria" and "scenarii". Should I be treating it as an Italian or Latin word?

Here are the stats from the Corpus of Contemporary American English and the British National Corpus:

           COCA    BNC

scenarios  3683    216
scenaria      0      0
scenarii      0      0

Merriam-Webster, Wiktionary, the American Heritage Dictionary of the English Language, and the Collins English Dictionary only mention scenarios.

I am sure they were hypercorrecting: http://www.google.com/search?q=scenario+plur

However they might have been old Italians:

http://fr.wikipedia.org/wiki/Sc%C3%A9nario

Le mot provient de l’italien scenario, « décor de théâtre ». En français, le mot s’est d’abord utilisé sans accent comme en italien, mais cet usage est archaïque.

Ni le pluriel italien archaïque scenarii (ancienne orthographe[1]), ni sa variante francisée scénarii (avec accent aigu) ne sont d'usage courant : le pluriel scénarios est le plus commun en français[2]. Selon l’Académie française, en effet, le mot scénario étant français (en italien, il n'aurait pas d'accent aigu), le pluriel « scénarios » s'impose - exactement comme pour lavabos ou pianos.[3]

The word comes from Italian scenario, “theatre scenery”. In French, the word was originally used without an accent as in Italian, but this is archaic.

Neither the archaic Italian plural scenarii (old spelling[1]), nor its French variant scénarii (with acute accent) is currently used: the plural scénarios is most common in French. Indeed, according to the Académie Française, since scénario is a French word (in Italian, there would be no acute accent), the plural scénarios is required — just as in lavabos, pianos.[3]

A Scenario in Italian is Sceneggiatura according to Wikipedia. Not what we are looking for here according to Francesco

Wiktionary reports that the plural of scenario is scenarios. It also reports that the "hypercorrect" plural of scenario is held to be scenarii (which is nonstandard and rare) since its etymology is Italian.

From scenario, the terminal o having been replaced with an i to form its plural, as per the Italian -o → -i pattern for forming plurals, by analogy with concerti and virtuosi. However, the plural of the Italian word scenario is scenari, making “scenarii” etymologically inconsistent.

According to Merriam-Webster and the OED, the accepted plural of scenario is scenarios. The Corpus of Contemporary American English reports 3683 instances of scenarios being used and none of scenarii.