If you self-publish, it shouldn't be any harder for you than for a U.S. native.
If you are trying to sell your book to a "traditional" publisher ... as @rolfedh says, it's hard for anyone who is not an established writer or already famous in some other field to get a publisher interested in his book. I don't know if it would be harder still for a foreigner per se, i.e. if a publisher would say, "Ohhhh, he's from Brazil, we don't want no grubby foreigners writing for us." :-)
A serious potential problem is if you are not fluent in English. For example, in your post, your English is pretty good, but I see two grammar errors: It should be "could be published worldwide", not "could be publish". And the sentence beginning "How, as a foreign writer ..." has no subject: it should be, "How, as a foreign writer, can I proceed ..." I don't know if this is a sign that your English is good but not fluent, or if you just typed the question hastily, etc. If you struggle with your English, this could really slow you down and interfere with concentrating on the story rather than language mechanics. In general, publishers are reluctant to publish books that don't have excellent grammar. There are exceptions and special cases, but it adds to the barriers that you have to overcome.
Another thing to consider is: What is the potential market in Brazil? Yes, there are many more people in the world who speak English than there are who speak Portuguese. But there are also many more books printed in English. I just found some stats that say there are 359 million people in the world who speak English and 260 million who speak Portuguese. I couldn't find stats on books published by language in a quick search, but I did find books published by country: US: 304,000, UK: 184,000, BR: 57,000, PT: 8,000. So there are maybe 359 million English speakers for 492,000 books, or 730 potential readers per book; and 260 million Portuguese speakers for 65,000 books, or 4,000 per book. The Portuguese market may be easier! (I have no idea how much Brazilians read versus how much U.S. folks read.)
Also, bear in mind that as a first-time author, the odds are that you will sell several hundred to a few thousand copies of your book. Yes, if your book is fabulous and you have good marketing and you are lucky you could sell millions of copies, but the odds are heavily against it.
I've published three books (in English) and I've only sold a handful of copies outside the U.S. (Including one in Brazil!)