A survey released Thursday showed 47 percent of CDU members favored Kramp-Karrenbauer, 37 percent supported Merz, and 12 percent favored Spahn.
Christian Democrats will vote Friday, in Hamburg, Germany, to decide who replaces Angela Merkel as party leader, and moves into pole position to succeed her as German chancellor in the future. Three candidates are competing for the position.
The first one is Annegret Kramp-Karrenbauer - who is popularly known as "mini Merkel" for being the Chancellor's protege - appears in the polls as the possible successor to Merkel.
Kramp-Karrenbauer 's views on migration are harsh and she promotes conservative values, denoted by her voting against the legislation that sponsored gay marriage in 2015.
"If we open the definition of marriage to homosexual couples, we will have to face other demands such as marriage between relatives or among more than two persons," Kramp-Karrenbauer said, according to the BBC.
The second most popular candidate, to replace Merkel, is Friedrich Merz. The Catholic lawyer - who owns one of the world's largest asset management company, BlackRock - wants tax cuts, greater integration of the European Union and seeks to reform the Euro area. Merz has also exhibited a very critical discourse against migrants, one which even questioned the constitutional right of asylum to all "politically persecuted."
"But for me it is clear that we can only solve the problems of immigration, migration and asylum in a European context," Merz said, to DW.
Recently, he also questioned whether Germany should sign the UN Global Compact for Migration at the upcoming Marrakech conference.
Finally, the third candidate is Jens Spahn, a 38-year-old party leader who has openly declared his homosexual preference. Spahn was elected to the Bundestag at age 22 and subsequently served as health minister.
A survey released Thursday showed 47 percent of Christian Democratic Union members favored Kramp-Karrenbauer, 37 percent supported Merz, and 12 percent favored Spahn.