Leading Sunni Shaikh Sayyed Saabiq of Al-Azhar stated that there is no single Hadeeth which can be considered as authentic suggesting that the Prophet (SAWA) ever crossed his hands during Salah (Fiqh Al-Sunnah).  That is why you find none of Sunnis is claiming folding or crossing the hands during Salah as Wajib and you find different verdicts among them. Imam Malik who is one of the four main Sunni Imams stated that the Salah of the Prophet (SAWA) and his companions after him is with open hands and never with holding or crossing hands. Imam Malik was asked about crossing hands in Salah, he replied: I don't know it , which means that it was not practiced by the Prophet nor his companions. (Al-Moghni by Ibn Qudamah, page 514).
'This crossing or folding hands was ordered first by Omar ibn al-Khattab when prisoners of war were brought from Persia to Madina and they did that as it was part of their culture or religious practice when they saw him as a sign of respect to the head of the state. He liked it and ordered his people to do it in Salah.(Jawahir Al -Kalam, V.11, page 19). Many leading companions rejected it as it was never done or approved by the Prophet (SAWA).

Imam Ali (AS) who is the best who knows about the Prophet, has repeatedly objected on crossing hands and called it emitting non Muslims as Jewish and Majoos fold their hands during their prayer. Imam Ali (AS): أسبلوا ولا تتشبهوا باليهود. أسبلوا ولا تتشبهوا بالمجوس Pray with your hands open and never imitate Jewish people. Keep your hands open while praying and never resemble Majoos.

Wassalam.