I'm bumping this thread because I'm serious about trying to construct a TL along these lines. On the language front, I'm already requesting books via different libraries on the Portuguese language, so that not only would I be able to have a basic grasp of the grammar (it shouldn't be hard, given my de facto second language is French), but also make myself familiar with any and all dialectal variation I can pluck. With respect to our Brazilian AH.commers (Gonzaga in particular), not every Portuguese variety spoken outside Portugal has to copy Brazil. So it's something I want to pursue. (Granted, for those familiar with my workload, it would be one of many TL projects I have, but I think I can handle them all.) Otherwise, I'd be interested to go ahead with this.
Now, it looks like that to pull it off, I'd need to pull off an early POD where no Treaty of Tordesillas would be needed and Portugal would have to back off from Brazil. That bit can easily be done. What then becomes the next step is figuring out not only how to get Portuguese people over (this shouldn't be hard, given that the Grand Banks attracted people of all sorts, and even with Portuguese colonization I don't see this attraction diminishing), but also two inter-related factors: how Portugal at this stage in the 1400s treats its Jewish people - and as I see it, Jews will play an important role in the story - and also how the Portuguese will have relations with the indigenous people here (or Aboriginals, or First Nations, or Native Americans, or whatever you want to call them). For some of them, there already is some memory of the earlier European presence with the Vikings (which is why the Beothuk, at first contact, tried to avoid Europeans as much as possible), so this is one barrier that would not only have to be overcome but also one that any Portuguese explorer would have to keep in mind.
So, having said that, what are your thoughts?