Does a Canadian need a visa to volunteer in Hawaii?

I just thought I would put in another answer, which absolutely directly answers what the OP is asking:

Does a Canadian need a visa to volunteer in Hawaii?

Answer: You cannot do this.

(Note - it's unfortunately misguided asking if you "need a visa", if you applied for one it would be instantly denied.)

In exceptionally limited circumstances, completely unrelated to everything you have described, visitors to the US can "volunteer" in situations such as floods, storms etc.

A friend wants to work on a farm

Answer: He cannot do this.

In exchange for the work

Answer: He cannot do this.

he will get meals and accommodation

Answer: He cannot do this.

Are these meals and accommodation considered payment

Yes.

Can it be considered a cultural exchange

"Cultural exchange" is utterly unrelated to anything mentioned here.

Purely FWIW, it is all-but impossible to get a Q visa ("cultural exchange") and note that you, a human, can't get one. Only businesses can get Q visas, on behalf of humans.

does he need a visa (for the scheme mentioned)

No visa of any type is available for the scheme mentioned.

Sorry for the incredibly bad news! :)

As everyone will say. Zillions of people a year visit the US in "gray areas". For example

• the most common question on this site is "When I visit the US as a tourist, can I in fact work remotely on my laptop". The answer is incredibly simple, "NO". There are no ifs ands or buts. You can NOT do that. BUT literally millions of people do that ever year.

• people ask things like "If I take photos in the US while a tourist, can I sell the photos". Answer is NO. But again hordes of people do this.

And so on.

So sure, vast hordes of people in this situation would simply say at the border (if even asked) "visiting friends" or just "holiday" and go their way. But be aware that border agents are extremely smart and experienced, the slightest whiff and you're done. There's zero debate, discussion.

Best of luck! Sorry for the bad news.

For "four months" ...

I've actually only now noticed OP mentions "for four months". It's really difficult to merely get tourism rights for "four months". wtt xngtng Canadians can in fact usually get up to six months tourism arranged in the US, so again assuming you're going to, well, lie "like everyone else" and just say it's tourism, should be achievable.

H2-A visa

As pointed out by MichaelS. There is an incredibly slim chance it could be done with a H2-A visa. Apart from anything else note that these take ~6 months to get and FWIW cost a couple hundred bucks. You'd also be, well, lying because it's inconceivable there's a specific labour shortage in question. (Might as well simply ... "arrive as a tourist and lie".) Generally H2-A are for well-known seasonal regional things, example, a well-known grape harvest month in region X. You'd have to convince the authorities that there's a sudden annual need for workers of type T in county C at XYZ time of year! But yes, MichaelS is right, you could theoretically do this.

You can only do volunteer work in the US as a visitor if that work is normally done by volunteers. You also cannot do any volunteer activity that benefits a commercial enterprise.

Unless the farm is a registered charity farm that normally has volunteers work for it this would not be allowed.

Your friend needs a visa that permits work.

See more details here: Is volunteer work allowed in the US while visiting under the VWP or a B1/B2 visa?

EDIT

As Joe points out, there are organizations like WWOOF where a visitor can participate in the experience of organic farming while receiving room and board. Since WWOOF advertises itself widely I assume it has taken legal advice to ensure that such visits are not classed as "work", volunteer or otherwise. I expect that the following are key:

1. The visitor helps "only a few hours a day";
2. The visitor is experiencing and being educated about organic farming
3. The benefit the farmer is getting is probably pretty small and not required (WWOOF specifically says "there is no requirement of productivity from the visitor")
4. The visits are short term

This probably allows WWOOF to characterize visitors as "tourists" and not "volunteer workers" (WWOOF specifically tell people to NOT say they are volunteers). It makes it more like a "dude ranch", where the visitor is there for the experience, and the fact that they experience herding and roping cattle (which some would class as 'work") makes it still a visitor experience. If your friend is doing this through an organization like WWOOF then take advice from them, not us.