Eastern Ukraine
According to a 2016 survey of religion in Ukraine held by the Razumkov Center, 73.5% of the population in Eastern Ukraine were Christians (63.2% Eastern Orthodox, 8.1% simply Christians, 1.0% Protestants, and 0.3% Latin Rite Catholics), 0.5% were Muslims, 0.3% were Jewish, and 0.3% were Hindus. Not religious and other believers not identifying with any of the listed major religious institutions constituted about 24.7% of the population. It also showed that approximately 55.6% of the population of eastern Ukraine (which in Razumkov's mapping excluded Donbass and consisted of the regions immediately to the west of it) declared to be believers, while 13.4% declared to be undecided or non-believers, and 3.5% declared to be atheist. 
A 2007 survey by the Razumkov Centre asked "Would you like to have your region separated from Ukraine and joined another state?" In eastern Ukraine, 77.9% of respondents disagreed, 10.4% agreed, and the rest were undecided. 
In a poll conducted by the Kyiv International Institute of Sociology in the first half of February 2014, 25.8% of those polled in East Ukraine believed "Ukraine and Russia must unite into a single state", nationwide this percentage was 12.5%.
History of Christianity in Ukraine
Protestantism arrived to Ukraine together with German immigrants in the 18th and 19th centuries. They were initially granted religious freedom by the Russian Imperial authorities, unlike the native population. While some were Catholic, the majority were either Evangelical (in North America known as Lutheran) or Mennonite (Anabaptist). Of the 200,000 or so Germans in Volhynia c.1900, some 90% or so were Lutheran. Lutheranism went into a major decline with the emigration of most of the Germans out of the region during the World Wars but there are still small remnants today (2006) in the Odessa and Kiev regions.