It's never official confirmed, but we could assume that he is, because of his Australian accent.

Original Kano concepts had him as an asian tough guy (i think he was suposed to be japanese... his name also endorses this nationality), but after he was portrayed by an Australian actor (at least he had that kind of accent), everybody started to look at him that way.

This nationality issue is reflected in Mortal Kombat Shaolin Monks and Armageddon, were Kano's accent is clearly Australian (i do believe that in Deception's Konquest, Kano also had Australian accent, although i haven't played that part of the game in some months now...).

It's like the Liu Kang & Kitana relationship, it was introduced in the first MK movie, and then assumed in MK4.

In Mortal Kombat: Deadly Alliance his Conquest narrator talks like an Australian... so my answer is yes.

"Kick him in the koskes!" and such

well he has the austrailian obviousness in him so i think so, he has no japanese characteristics but not to say that was what his first concept was. but since we all no he is no where close to the japanese heritage, hes austrailian.

it really wasnt until the movie came out and the actor who played kano was austrialian. I believe it was after that was when they gave him austrialian voice in the games

If I remember correctly Kano was born in Japan but taken from his mother and was raised in the United States.