All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
On the other hand, if you pray alone, then it is also permissible to supplicate with the Qunut supplication using the plural pronoun with the intention of including your Muslim brothers as well; this is the opinion preferred by Shaykh Al-Islam Ibn Taymiyyah . Al-Mardaawi
from the Hanbali School of Fiqh, said in Al-Insaaf: “The person who prays on his own uses the singular form of the pronoun, according to the correct view of the School, but Shaykh Taqiy Ad-Deen (i.e. Ibn Taymiyyah) is of the opinion that he does not use the singular form but he uses the plural form because he supplicates for himself and for the Muslims.”
On the other hand, the Qunut supplication was reported with the singular form in some narrations and in some other narrations, with the plural form; for instance, the narration by At-Tabaraani reads: “O Allaah, guide us along with those whom You have guided, pardon us along with those whom You have pardoned, be an ally to us along with those whom You are an ally to, and bless for us that which You have bestowed upon us. Protect us from the evil that You have decreed, for verily You decree and none can decree over You. For surely, he whom You show allegiance to is never abased and he whom You take as an enemy is never honored. Blessed and Exalted are You, our Lord."
Also, the narration by Ibn Hibbaan reads: “I heard the Prophet supplicating with this supplication: "O Allaah, guide us along with those whom You have guided, pardon us along with those whom You have pardoned, be an ally to us along with those whom You are an ally to...”
For more benefit, please refer to Fatwa 89397.
Allaah Knows best.