a-tún (spanish) or to-nyi-na (català)
too-na for me
Everyone in my neck of the woods pronounces it too-na.
Tuner or chewna, both sound the same 
Or Tsuna lol. They are basically the same just spelt different.
You can tune a piano but you can’t tune a fish.
Choona
Too-nah inna cahn, a-yuh!
“It’s not a too-na’ (Arnie)
I fear I might just be a poshly spoken Brit :o
http://www.macmillandictionary.com/pronunciation/british/tuna
Tuna, with a U.
Ah i didn’t realise the poster is kiwi. Maybe we can also ask how to pronounce fish and chips? lol 
Chicken Of The Sea
Nothing like a good too-na steak seared on the outside, rare on the inside!
a Chicken of the sea
In Hawiian it’s “humahumanupanupaapua’a” 
Phil
Tune-Ahh
John.
Wow, I don’t care how you pronounce it, there’s a lot of money in that net!
Like this.