This verse does not mean anyone who is guardian of (regardless of if they are believer or not) are Mutaqoon (pious men). But it mean its real guardians are Mutaqoon. So we should seek who are Mutaqoon. So firstly we should know what Taqwa is and then check who has the attributes of Taqwa.
A sermon of Imam Ali in response of Hammam when he asked Imam to describe Mutaqoon in such a way that as if he see them is known as best source for definition and knowing Mutaqoon.
This sermon can be read here:
Sermon 193 It is related that a companion of Amir al-mu'minin called Hammam who...
This sermon is famous and is recorded in many shia and sunni books. For example:
(1) Kitab Sulaym ibn Qays, 211;
(2) al-Saduq, al-'Amali, 340;
(3) Ibn Qutaybah, `Uyun, II, 352;
(4) al-Harrani, Tuhaf, 159;
(5) Sibt ibn al-Jawzi, Tadhkirah, 148;
(6) Ibn Talhah, Matalib, I, 151;
(7) al-Karajiki, Kanz, 31;
udi, Muruj, II, 420.Abd al-Zahra' mentions 8 commentaries on this famous khutbah al-Qasi`ah.
Some parts of this sermon:
Thus, the God-fearing, in it are the people of distinction. Their
speech is to the point, their dress is moderate and their gait is
humble. They keep their eyes closed to what Allah has made unlawful
for them, and they put their ears to that knowledge which is
beneficial to them. They remain in the time of trials as though they
remain in comfort. If there had not been fixed periods (of life)
ordained for each, their spirits would not have remained in their
bodies even for the twinkling of an eye because of (their) eagerness
for the reward and fear of chastisement. The greatness of the Creator
is seated in their heart, and, so, everything else appears small in
their eyes. Thus to them Paradise is as though they see it and are
enjoying its favors. To them, Hell is also as if they see it and are
suffering punishment in it.
Then you asked about interpret of this verse according to Shia. Here is an English commentary of Shia about this verse:
[Pooya/Ali Commentary 8:34]
The true custodians of the masjid al haram are the divinely
commissioned guardians of faith- the Imams of the Ahl ul Bayt. After
the Holy Prophet there is no one equal to them in taqwa (piety) (see
commentary of al Baqarah: 2).