New Zealand is a strong and well performing team Sri Lanka has just joined the string of strength so we cannot consider Sri Lanka to be strong compared to New Zealand. Yes they have managed to beat New Zealand in some matches but they will not be considered fully strong.New Zealand was the only weakness in this but now they will not give any chance to Sri Lanka and we can judge that from this ODI match.
Now see here that Sri Lanka could score only 178 runs. And the New Zealand batsmen have won the match by achieving this target in 26 overs and you can see the pressure from the New Zealand bowlers as they dismissed the entire team in 43 overs and stop the runs as well. Sri Lanka suffered a huge loss.
I consider New Zealand as the favorite in this series. New Zealand is a strong team. At the same time, this is New Zealand's home series. However, if the series was held in Sri Lanka, I would consider Sri Lanka as the favorite. Because in the last few series, we have seen Sri Lankan players perform well in home matches. But the performance of Sri Lankan players has deteriorated on pace-friendly pitches outside the country. In the series against New Zealand, we can also see irregular performance from Sri Lankan players.
Sri Lanka lost the first two matches in the T20 series. However, Sri Lanka gave a big target of 200+ in the last match and won. That is why many thought that the ODI series would also be exciting and Sri Lanka would play well. But Sri Lanka lost badly in the first match. I do not think New Zealand will face any major obstacles in winning this series.