Since Baltic States were under different rules there were believers of different religions.
Lutheranism is present in Latvia due to strong historical links with the Sweden and Germany, Catholicism is most prevalent in Eastern Latvia (Latgale), due to Polish-Lithuanian influence. The Orthodox Church plays also a big role in Latvia because of Russian, Ukrainian and Belarusian minorities. At Soviet times many people stopped following any religion so there are many agnostic and atheist people as well.

Unfortunatelly I wasn't able to find any recent statistics(I don't trust surveys), the last one I found was from 2011.

According to this stats the estimate percentages looked like this:
Lutheranism - 34.3%
Catholic Church - 25.1%
Eastern Orthodoxy and Old Believers - 19.4%
Other Christians - 1.2%
Agnostic & Atheists - 20.0%

As form of intersting fact, there is neo-pagan movement called Dievturība basing on myths and dainas. It has just 600 - 800 active members

To sum up, Latvia doesn't have any religion that would gather majority of people living in Latvia, though all the groups are Christian(Lutheran, Catholic and Orthodox). Also there is high amount of Agnostic and Atheist people. It is effect of being ruled by many countries throughout the history.