Stanley earned an exemption based on his world ranking of 60. The USGA held six spots in the field for those players who could potentially break into the top 60 but the 26-year-old winner of last year's Phoenix Open was the only player to break the threshold.
Therefore five alternates from sectional qualifying complete the 156-player field. Weir, Harold Varner III, Ryan Palmer, Ryan Yip and Rikard Karlberg.
Canadian Weir, the 2003 US Masters champion, will played in the event for the 13rd time while Karlberg was the first alternate from the England sectional at Walton Heath last month.
The tournament begins at Merion Golf Club in Ardmore, Pennsylvania on Thursday.