Imam Dhahabi said:
حَسْبُكَ بِمَنْ يُؤَمِّرُهُ عُمَرُ، ثُمَّ عُثْمَانُ عَلَى إِقْلِيْمٍ - وَهُوَ ثَغْرٌ - فَيَضْبِطُهُ، وَيَقُوْمُ بِهِ أَتَمَّ قِيَامٍ، وَيُرْضِي النَّاسَ بِسَخَائِهِ وَحِلْمِهِ
It is enough for the virtues of Saydna Muawaiya that he was appointed governor by Saydna Umar and then Usman, he was inexperience at that time however he managed his area of governance and administrated with full trust and pleased people with his generosity and calmness.
[Seyr alam an Nubala 3/132]
Saydna Umar was intelligent and just in appointing someone as a governor under his Caliphate as it reflects in his saying:
«اللَّهُمَّ إِنِّي أُشْهِدُكَ عَلَى أُمَرَاءِ الْأَمْصَارِ، وَإِنِّي إِنَّمَا بَعَثْتُهُمْ عَلَيْهِمْ لِيَعْدِلُوا عَلَيْهِمْ وَلِيُعَلِّمُوا النَّاسَ دِينَهُمْ وَسُنَّةَ نَبِيِّهِمْ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ، وَيَقْسِمُوا فِيهِمْ فَيْئَهُمْ، وَيَرْفَعُوا إِلَيَّ مَا أَشْكَلَ عَلَيْهِمْ مِنْ أَمْرِهِمْ»
O' Allah I bear you witness on these governors of cities that I only appointed them to be just with the people and teach people about deen and sunnah of Nabi صلی اللہ علیہ وسلم and distribute the spoils of war among them and if they face any issues then refer to me to resolve.
[Sahih Muslim #1557, #567]
This shows how Saydna Umar appointed his governors after carefully examining them and considered only those who were most worthiest.
Imam ibn Taymiyah said:
وَعُمَرُ مِنْ أَعْلَمِ النَّاسِ بِأَحْوَالِ الرِّجَالِ، وَأَحْذَقِهِمْ فِي السِّيَاسَةِ، وَأَبْعَدِ النَّاسِ عَنِ الْهَوَى، لَمْ يُولِّ فِي خِلَافَتِهِ أَحَدًا مِنْ أَقَارِبِهِ، وَإِنَّمَا كَانَ يَخْتَارُ لِلْوِلَايَةِ مَنْ يَرَاهُ أَصْلَحَ لَهَا ; فَلَمْ يُوَلِّ مُعَاوِيَةَ إِلَّا وَهُوَ عِنْدُهُ مِمَّنْ يَصْلُحُ لِلْإِمَارَةِ
Saydna Umar was well knowledgeable about the affairs of people, and brilliant in the political matters, and far from the worldly desires. During his Caliphate he never appointed anyone from his close relatives as a governor. Certainty, he appoints an individual as a governor to whom he finds worthy, which is why he appointed Saydna Muawiya as a governor because he found him worthy.
[Minhaj as Sunnah 8/134]
