Which country would you advise me to do an English exchange program?

come to Canada, B.C or Alberta where everything costs so much $$$$$$$$$$$$$$$$$$$$$$$

USA! USA!

Canada really good and i alway dream to come that place and norway too

It kinda depends on what you like and find interesting. And what temperature.

In May it's heading into winter in New Zealand and Australia (but not such a problem in Brisbane or Perth).

My picks for cities
London or New York would be heading into summer. With tons to see and do. Amazing places to visit if you haven't already.
Auckland, New Zealand (where i live) is ALOT quieter. A few things to see but tourism here is more about taking journeys for scenery or physical activity (surfing, tramping, biking, bungee, skiing etc). Public transport is very weak here also.
A city that I really enjoyed visiting recently was Sydney, Australia. Good weather and just a ton to see in and around the city.

England could be good, that way you can also visit a lot of different countries easily :)

Like so many I vote Canada as well. But, I'm throwing in a vote for the East coast. It's quiet, friendly and homey. I've traveled East to West and across the North, and really, you shouldn't have an issue finding a place to your liking.

Maybe just do the US? Idk, that's really all I can think of

Come see us in Canada. In the winter.
Muhahahah.

I've always wanted to travel to the UK myself. That would be my choice. Have fun wherever you go:)

If one wants to learn the Queens English there really is only one place one should visit and that my good man is England. The problem is depending on which part of our fair nation you visit you may learn a more localized version of the Queens English with local slang as is the norm these days.

How ever do take into account cost of said trip and Jet lag a tired brain is less perceptive to learning.

Canadaaa!

Go to Vancouver, B.C. in Canada.

I like being that guy so unless someone has said it before me, here's a free lesson from an unaccredited instructor:

English is the de jure official language at the national level only of Canada (though some states in the USA have English as an official language). English is only the de facto official language of the rest of those countries (English is a de jure official language of Ireland--it is only a de factor official language of the United Kingdom).

Also, unlike many other languages, such as Spanish or French, there is no official authority that can dictate rules governing the English language.

I hope my pedantry was appreciated.

Anyway, you're Brazilian, and I'd say go to the USA. It's the culture you've almost certainly been exposed to the most by far and now you get to have your perceptions of it smash up against the reality of personal experience. I would argue the same for most anyone in the western hemisphere from a Latin American country asking the question: go to USA.

Also, there are other similarities between Brazil and the US; both are 'New World' former colonies, recipients of millions of disenfranchised from the Atlantic slave trade, and dominate to a degree their continent by population and land mass (sorry Canada, you're America's hat, and while you are huge most of you is frozen).

I don't know if you're Afro-Brazilian or not and maybe this last bit of rationale is more or less persuasive because you are/aren't, but that's just my take on things.

I'd say since this is a rather unique opportunity that you may not have again. Base your decision on what trip will give you the most interesting experience. But consider accessibility aswell, sometimes its nice to be able to spread your wings and touch on different cultural experiences in the process.

The benefits of Europe is that everything is much closer together. Which is well worth considering.

England/UK, which is where I'd definitely go, hehe. Or, the US... I suppose this country isn't too bad.

I'd like canada or england or ireland

I would say that:
Don't listen to what others recommend you. Google all that countries and see which of them seems most exotic and "unknown" culturally for you. Then pick it and enjoy expanding horizons and learning about different world!

Since English is the main language in all of them, you will improve it anyway, and what accent you gain by the way doesn't really matter.

Of course, Ireland !

To propose something different: Have you considered Malta?
English is an official language. I don't know if you can fill 4 weeks well there, but there is plenty to see and do.
No, I don't live there, but I've been there on holiday before :)