None of the Quraish was forced to become Muslim, but Muhammad’s victory convinced some of his most principled opponents, such as Abu Sufyan, that the old religion had failed. 
A quick recap on Abu Sufyan bin Harith bin Abdul Muttalib
He was the cousin of the Prophet (p) as well as his foster brother. He was a poet who antagonized Prophet Muhammad (p) during his Prophetic mission.
His enmity to the Prophet (p) degenerated into full scale war against him on the field of battle. He would also make fun of him with his tongue at public gatherings until light of Iman (faith) entered his heart and his breast became expanded for the acceptance of Islam. 
The expert, Sheikh Al Mubarakpuri, on Abu Sufyan’s conversion
When piecing together actualities from the plethora of early traditions we need EXPERTS to sift through them and analyse and subsequently conclude according to a criterion of reliability, context and a process of harmonization.
Sheikh Safiur Rahman al Mubarakpuri describes the conversion of Abu Sufyan:
After making full preparation, the Prophet (p) proceeded to Makkah at the head of ten thousand soldiers on the 10th of Ramadan 8 AH… 
…At Al-Abwa, the Muslims came across Abu Sufyan bin Al-Harith and Abdullah bin Umaiyah, the Prophet’s cousins, but, on account of the harm they had inflicted, and their satiric language against the believers, they were not welcomed. 
Ali (ra) addressed Abu Sufyan to go and request the Prophet (p) for pardon and confess his ill-behaviour in a manner similar to that of the brothers of Yusuf (the Prophet Joseph, p):
“They said: ‘By Allah! Indeed Allah has preferred you above us, and we have been sinners’” [12:91]
Abu Sufyan followed Ali’s advice , to which the Prophet (p) quoted Allah’s Words:
“He said: No reproach on you this day, may Allah forgive you, and He is the Most Merciful of those who show mercy!’” [12:92]
Abu Sufyan recited some verses paying a generous tribute to the Prophet (p) and professing Islam as his only religion  
So this was the point Abu Sufyan accepted Islam – clearly he was NOT forced to accept Islam, despite there being threats to his life as well as opposition to him due to his past . In fact Abu Sufyan’s wife converted to Islam as well despite having chewed the liver of Hamza (the Prophet’s uncle) 
Abu Sufyan’s conversion described by Sa’d Yusuf Abu Aziz
Sa’d Yusuf Abu Aziz also describes Abu Sufyan’s conversion which clearly illustrates Abu Sufyan was intent on gaining the pleasure of Prophet Muhammad (p) – he was not coerced at the point of a sword:
The light of faith shone into the heart of Abu Sufyan while the Messenger of Allah was preparing for the conquest of Makkah. Abu Sufyan and his son, Ja’far left Makkah for Madinah with the sole intention of submitting to the Lord of the worlds. When the Prophet (p) saw him, he turned away from him. He humbled himself before the Prophet (p) imploring him for the pleasure. He would earn his pleasure or else he would hold the hand of his son and both of them would walk in the wilderness until they would die of hunger and thirst.
The Prophet eventually relented toward him and he became a good Muslim afterwards. 
Abu Sufyan’s conversion was sincere
Of course, if a conversion is forced it is not going to be a faithful “conversion”. Abu Sufyan’s conversion was sincere, so much so that he even put his life on the line by standing firm in protecting the Prophet (p) in the Battle of Hunayn 
Abu Sufyan’s sincerity in Islam is highlighted further by his words at the time of his passing away:
Abu Ishaq As-Sibai said: when Abu Sufyan bin Al Harith bin Abdul Muttalib approached his death he said “Do not weep over my death for since I became a Muslim, I have not been tarnished” 
Islamophobes isolate narrations and add their agenda-based spin to such in order to prop up their misguided argumentation. We should always be mindful of learning from those who are privy to more knowledge than folk on Islamophobic forums. The SCHOLARS are people we should be relying upon for Islamic instructions and teachings.
The Quran teaches us there is no compulsion in religion
There is no compulsion in religion. The right direction is henceforth distinct from error. And he who rejecteth false deities and believeth in Allah hath grasped a firm handhold which will never break. Allah is Hearer, Knower [Quran 2:256, Pikthal translation]
 Abu Sufyan accepted Islam at this point and thereafter became a good Muslim. The Prophet (p) loved him and even testified that he would be in Paradise. See Zadul-Ma’ad 2/162. 163 (Footnote from page 462 of Arraheequl Makhtoum, Safiurrahman Al Mubarakpuri, Darusslam, 2002)
 Islam – A Short History, Karen Armstrong, Phoenix Press, 2001, p20
 Sa’d Yusuf Abu Aziz, Men and Women around the Messenger (p), Darussalam, 2009, p281- 282
 Arraheequl Makhtoum, Safiurrahman Al Mubarakpuri, Darusslam, 2002, 461-462
 Before they got near the camp, they met Abbas (ra), the Prophet’s uncle. He informed Abu Sufyan of the situation and advised him to accept Islam and persuade his people to surrender before Muhammad (p); otherwise his head would be struck off.
Under the prevailing compelling circumstances, Abu Sufyan went in the company of Abbas (ra) seeking the chance of meeting the Prophet (p). The Muslims were furious to see Abu Sufyan and wanted to kill him on the spot. But the two men managed, not without difficulties, to see Allah’s Messenger (p) who advised that they see him the following day. The Prophet (p) addressed Abu Sufyan saying “Woe to you! Isn’t it time for you to bear witness to the Oneness of Allah and Prophethood of Muhammad?” Here he began to request the Prophet (p) in the most sincere words that testify to the Prophet’s generosity and mild temper begging for pardon and forgiveness, and professing wholeheartedly the new Faith.
[Arraheequl Makhtoum, Safiurrahman Al Mubarakpuri, Darusslam, 2002, p462-463]
 Upon the conquest of Mecca, the Meccans gathered to pledge loyalty to the Prophet (p), this included the wife of Abu Sufyan:
…Hind bint Utbah, Abu Sufyan’s wife, came in the group of women disguised lest the Prophet (p) should recognize and account for her, having chewed the liver of Hamzah (ra), his uncle.
The Prophet (p) accepted their allegiance on condition that they associate none with Allah, to which they immediately agreed. He added that they should not practice theft. Here Hind complained that her husband, Abu Sufyan, was tight-fisted. Her husband interrupted granting all his worldly possessions to her. The Prophet (p) laughed and recognized the woman. She requested him to extend his pardon to her and to forgive all her previous sins. Some other conditions were imposed including the prohibition of adultery, killing of infants or fabricating falsehood. To all these orders, Hind replied positively swearing that she would not have come to take an oath of allegiance if she had had the least seed of disobedience to him. On returning home, she broke her idol admitting her delusion over stone-gods.
[Arraheequl Makhtoum, Safiurrahman Al Mubarakpuri, Darusslam, 2002, p470-471]
 Abu Sufyan was by the side of the Prophet (p) holding the rein of his riding animal fending off attacks against the Prophet (p). When the dust of the intense battle subsided and the Muslims obtained a resounding victory, the Messenger of Allah became even more fond of Abu Sufyan. He was amongst those who were steadfast with him on that day. He demonstrated the sincerity of his Islam. [Sa’d Yusuf Abu Aziz, Men and Women around the Messenger (p), Darussalam, 2009, p283]
 Sa’d Yusuf Abu Aziz, Men and Women around the Messenger (p), Darussalam, 2009, p284