In our case elections work by having two "rounds", in the first one the top 2 candidates go to the second round, and then people vote for one or the other.

This means that the "vote division" thing is not really an issue... If you end in second place, you still get a shot to get all the votes of whoever doesn't want to vote for the first place.

Thus basically any candidate in second place trying to campaign saying the vote will be "divided" is basically bullshitting the voter base in an attempt to secure his second place.

The first place DO want to concentrate votes though, if you end with more than 50% of the votes (and Brazil has mandatory voting, so basically 50% of voters) then you win outright, so sometimes parties DO attempt to do this by pooling all their votes toward one candidate (for example several xxx-wing parties choosing only one candidate among them all and campaigning all of them for that same guy).