In Brazil .com.br is the norm, but there are plenty of other third levels under .br.
I would be surprised .br.com really gets a measure of use there, promoting your domains might even drive traffic to the .com.br counterparts, not to mention the branding nightmare if you have ambitions. I think .br.com will always drag you down.
Honestly I have nothing good to say about the Centralnic domains, it's a newbie trap imho. I would never develop anything meaningful on a private subdomain, on top of that it is more expensive than a real extension.
The best would be to ask local people or run a survey.
I would do like this: first show them the URL, then tell them to visit the site. This is to verify that they remember the name correctly (especially the 'TLD' that is in reverse order, it's not what they are used to).
Then give them the business card so they have the name in print in front of their eyes, and see how many will 'correct' the .br.com to .com.br.
Whatever you do, it's very important to understand the local conditions and peculiarities when investing in foreign markets.
