I’m not going to get my panties in a bunch over some deacons chosing to pray the Our Father in the orans position. However, please take note of the following:
"the Holy See has been concerned about the laity unduly aping the priest at Mass, and in the 1997 Instruction on Collaboration, an unprecedented conjunction of Vatican dicasteries wrote:
[INDENT]6 § 2. To promote the proper identity (of various roles) in this area, those abuses which are contrary to the provisions of canon 907 deacons and lay persons are not permitted to say the prayers, especially the eucharistic prayer, nor to perform the actions which are proper to the celebrating priest."] are to be eradicated. In eucharistic celebrations deacons and non-ordained members of the faithful may not pronounce prayers — e.g. especially the eucharistic prayer, with its concluding doxology — or any other parts of the liturgy reserved to the celebrant priest. Neither may deacons or non-ordained members of the faithful use gestures or actions which are proper to the same priest celebrant. It is a grave abuse for any member of the non-ordained faithful to “quasi preside” at the Mass while leaving only that minimal participation to the priest which is necessary to secure validity. (emphasis partially mine)
This instruction, incidentally, was approved by John Paul II in forma specifica, meaning that the pope invested it with his own authority and is binding on us with the pope’s authority and not merely the authority of the authoring congregations.
Now, what gestures are proper to the priest celebrant? The orans gesture when praying on behalf of the people is certainly one of them. The priest celebrant and no others (not even concelebrating priests) are directed to make this gesture in the rubrics.
In some places, some laity may spread their arms whenever the priest spreads his in a kind of “Back atcha!” motion. I’ve even seen some do a phenomenal pantomime of tossing an invisible ball to the priest by swooping their palms close together and then spreading them apart as they assume the orans posture. But this is clearly apart from the rubrics.
If the orans posture is one proper to the priest celebrant in the liturgy then the laity should not be imitating it."
Commenting further on this, Father Colin Donovan has this to say:
“The liturgical use of this position by the priest is spelled out in the rubrics (the laws governing how the Mass is said). It indicates his praying on BEHALF of us, acting as alter Christus as pastor of the flock, head of the body. It used to be minutely defined in the rubrics, which now say only, “extends his hands” or “with hands extended.” Priests understand what is meant (from observation and training), and although there is some variability between priests basically the same gesture is obtained from all of them by these words.
In the rubrics the Orans gesture is asked principally of the Main Celebrant, but on those occasions where either a priestly action is done (Eucharistic Prayer) or prayer in common (Our Father) all the concelebrants do it.
It is never done by the Deacon, who does not represent the People before God but assists him who does.” (emphasis added)