Having good companionship toward all people whether they agree with us in opinion or disagree is incumbent, specially, Sunni Muslims who are from Islamic society.
Question:
How should be Shia's behavior toward Sunnis?
Answer:
In Ahl al-Bayt's (A) point of view good companionship toward all people whether they agree with us in opinion or disagree is incumbent. And for this reason when Imam Ali (A) saw a non-Muslim off, in response of his question about this behavior said: "seeing the one off at the moment of separation to respect him is high level of good companionship."[1]
Moreover our Imams have Recommended us to say hello to non-Muslims [2] let alone Sunnis who are considered from Islamic society.
Muawiyah ibn wahab asked Imam Sadiq (A):"how we should behavior toward the people who aren't from our faith?"
Imam replied: "follow your Imams. By Allah! They visit their patients, attend their funeral, testify against them or in their favor and repay their loans." [3]
Finally, Sunnis like Ahl al-Bayt as well, and don't curse them.
Note:
[1] al-kafi, v.2, p.670 "هذَا مِنْ تَمَامِ حُسْنِ الصُّحْبَةِ أَنْ يُشَيِّعَ الرَّجُلُ صَاحِبَهُ هُنَيْئَةً إِذَا فَارَقَه"
[2] al-kafi, v.2, p.649 "سَأَلْتُ أَبَا عَبْدِ اللَّهِ علیه السلام عَنِ الْيَهُودِيِّ وَ النَّصْرَانِيِّ وَ الْمُشْرِكِ إِذَا سَلَّمُوا عَلَى الرَّجُلِ وَ هُوَ جَالِسٌ كَيْفَ يَنْبَغِي أَنْ يَرُدَّ عَلَيْهِمْ فَقَالَ يَقُولُ عَلَيْكُمْ"
[3] al-kafi, v.2, p. 636 "قَالَ تَنْظُرُونَ إِلَى أَئِمَّتِكُمُ الَّذِينَ تَقْتَدُونَ بِهِمْ فَتَصْنَعُونَ مَا يَصْنَعُونَ فَوَ اللَّهِ إِنَّهُمْ لَيَعُودُونَ مَرْضَاهُمْ وَ يَشْهَدُونَ جَنَائِزَهُمْ وَ يُقِيمُونَ الشَّهَادَةَ لَهُمْ وَ عَلَيْهِمْ وَ يُؤَدُّونَ الْأَمَانَةَ إِلَيْهِمْ"