When Hazrat Imam Jafar (as) married Hazrat Abu Hanifa’s sister then why can’t a Syed and Shia marry a sunni girl? Why there are man made differences? Neither Hazrat Imam Jaffar (AS) nor Imam Abu Hanifa (RA) wrote Fiqah Jafferia and Fiqah Hanfia, when we all know it was the propaganda of Abbasis then why are Ulma not preaching this to nation?

Imam Ja'far Sadiq (AS) married with Fatima, who was a descendant of Imam Hassan Ibn Ali (a.s) From her two sons were born named Ismail bin Ja'far (the sixth Imam of the Ismaili sect) and Abdullah Afteh. After the demise of Fatima, he married with Hamideh khatoon and taught her religious matters as she became one of the learned woman in Madina. Hamideh khatoon gave birth to two sons named Musa Kazim(a.s) (the seventh Imam of the Twelver Shiites) and Mohammad Dibaj.

Therefore there is no evidence that Imam Sadiq (a.s) had married with the sister of Abu Hanifa.

Janab Abu Hanifa was a student of Imam Sadiq (a.s) so his knowledge was from Imam Sadiq (a.s) but what Imam Sadiq (a.s) had learnt was from Allah (swt) and none can prove in the entire history that anyone who had taught Imam Sadiq (a.s).

Yes I’m do agree with you that when there no such restrictions exist in Shariya that Shia can’t marry with Sunni and Sunni can’t marry with Shia then we should not implement islamic laws from our own side.

But as we know that according to many traditions and Quranic verses Wilayat is and integral part of Islam and Holy Prophet (saww) has appointed Ameeral Momenin Ali(a.s) as his successor by the command of Allah (swt) :

يَا أَيُّهَا الرَّسُولُ بَلِّغْ مَا أُنزِلَ إِلَيْكَ مِن رَّبِّكَ وَإِن لَّمْ تَفْعَلْ فَمَا بَلَّغْتَ رِسَالَتَهُ وَاللَّهُ يَعْصِمُكَ مِنَ النَّاسِ إِنَّ اللَّهَ لَا يَهْدِي الْقَوْمَ الْكَافِرِينَ
O APOSTLE! Announce all that has been bestowed from on high upon thee by thy Sustainer: for unless thou doest it fully, thou wilt not have delivered His message [at all]. And God will protect thee from [unbelieving] men: behold, God does not guide people who refuse to acknowledge the truth.

Then there is a big challenge if the offspring from a Sunni father will not accept Wilayat of Ameer al Momenin (a.s) and instead they will have love of Muawia like person who the open enemy of Ahlulbayt (a.s) then who will be responsible? Yes we respect and love our Sunni brothers who loves Ahlulbayt (a.s) but we can’t accept Muawia bin Abu Sfiyan like person as a leader.