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According to this article Prime Minister Mia Mottley is seen as a likely front runner.
I've made a market on who the actual person will be:
There is a general principle that the SG position rotates among regional groups. António Guterres being from Portugal makes it unlikely that the next SG will come from the Western European and Others Group (which includes Canada). There has never been a SG from the Eastern European Group, but that group kinda doesn't really make sense anymore now that the region is free from Soviet occupation. There is also an unwritten norm that citizens of the permanent members of the Security Council cannot be SG, so if anyone wants to vote France even lower than I did, go for it.
Guterres is from Portugal;
Ban Ki-Moon is from South Korea;
Kofi Annan was from Ghana;
Boutros Boutros-Ghali was from Egypt (I think the fact he only served one term, besides being from an Arab-majority African country as opposed to a Sub-Saharan one, justified having two consecutive SGs from Africa. It probably didn't matter that Boutros-Ghali himself was not Arab but Copt);
Javier Pérez de Cuellar was from Peru;
Kurt Waldheim was from Austria, so the rotation has reached Europe again with Guterres.
Therefore, I think it is likely that the next SG will come from Latin America and the Caribbean. Brazil made successful campaigns to nominate the Directors-General of FAO and the WTO, and they would very much like to have a Brazilian as SG. Alternatively, Michelle Bachelet might be a candidate as well.
@BrunoParga cnn agrees, Latin America or Caribbean.
"Historically, there has been a geographical rotation for the position, so it seems likely the next UN leader will be from the Latin America and the Caribbean region"