Buchanan, who was in charge when Australia won the 50-over tournament in 2003 and '07, said the likely finalists would come from either AB de Villiers' Proteas or the co-hosts of the showpiece.
The 61-year-old, who has served as a consultant to England and as director of New Zealand Cricket since stepping down as Australian coach in 2007, said the 2015 tournament has no clear favourite.
"It looks a reasonably open tournament," Buchanan said.
"Australia, New Zealand, South Africa probably are the ones that head the list.
"Obviously India and England haven't necessarily played all that well out here at the moment, but you don't want to be playing your best cricket right now, and there's still some trial games to get through.
"Sri Lanka and Pakistan have been a little bit disappointing in New Zealand, but again, someone like Pakistan is a team that the longer they can go into a tournament, the more dangerous they become.
"Sri Lanka have still got some very good players that have played out here a lot, and they play in New Zealand a bit as well. So I expect them to be there or thereabouts.
"But I think at this point in time, Australia, New Zealand and South Africa loom as the likely finalists, but I think if the draws go as expected, one of those will be knocked out in the semi-final stage."
Buchanan said the one danger of Australia's hosting rights is players being distracted by nearby friends and family.
While the former coach conceded time spent outside the World Cup squad and bubble is healthy, Buchanan also said there was a risk of distraction.
"In terms of camaraderie, I think that could be affected in Australia if players choose to head back to home ports because all that does is add a heck of a lot of travel," Buchanan said.
"And in terms of why you're doing, the 'getting away part' is just so that you can freshen up, so that you don't have to necessarily be engaged in anything that may drain you in terms of mental and physical, and importantly get you away from cricket."