Ireland internationals O'Brien and Earls have been exemplary for their respective provinces and both were prominent in the Six Nations campaign.
Leinster's Nacewa has excelled at full-back this season as Rob Kearney has been absent through injury since November.
Meanwhile, Munster scrum-half Conor Murray, Leinster back-row Rhys Ruddock and Ulster centre Nevin Spence are the candidates for the IRUPA Young Player of the Year.
The winners will be announced at the players' body awards ceremony on Wednesday, 4 May
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