Create script to use canvas size to square the image by the largest dimension.

Here is a script to make the image square, using the longest side of the image, then using content aware fill.

#target photoshop

var savedRuler = app.preferences.rulerUnits; //save the current ruler units

app.preferences.rulerUnits = Units.PIXELS; 

var doc = activeDocument

var newSize = Math.max(doc.width.value,doc.height.value);
var topS,leftS,bottomS,rightS

if(doc.width>doc.height){
    topS = -(newSize-doc.height.value)/2;
    leftS = 0;
    bottomS = (newSize-doc.height.value)/2 + doc.height.value;
    rightS = doc.width.value;
    cropContentAware ();
    }
else if(doc.height>doc.width){
    topS = 0;
    leftS = -(newSize-doc.width.value)/2;
    bottomS = doc.height.value;
    rightS = (newSize-doc.width.value)/2 + doc.width.value;    
    cropContentAware ();
    }
else{}

app.preferences.rulerUnits = savedRuler; //restore the original ruler units

function cropContentAware(){
    var idCrop = charIDToTypeID( "Crop" );
        var desc363 = new ActionDescriptor();
        var idT = charIDToTypeID( "T   " );
            var desc364 = new ActionDescriptor();
            var idTop = charIDToTypeID( "Top " );
            var idPxl = charIDToTypeID( "#Pxl" );
            desc364.putUnitDouble( idTop, idPxl, topS );
            var idLeft = charIDToTypeID( "Left" );
            var idPxl = charIDToTypeID( "#Pxl" );
            desc364.putUnitDouble( idLeft, idPxl, leftS );
            var idBtom = charIDToTypeID( "Btom" );
            var idPxl = charIDToTypeID( "#Pxl" );
            desc364.putUnitDouble( idBtom, idPxl, bottomS );
            var idRght = charIDToTypeID( "Rght" );
            var idPxl = charIDToTypeID( "#Pxl" );
            desc364.putUnitDouble( idRght, idPxl, rightS );
        var idRctn = charIDToTypeID( "Rctn" );
        desc363.putObject( idT, idRctn, desc364 );
        var idAngl = charIDToTypeID( "Angl" );
        var idAng = charIDToTypeID( "#Ang" );
        desc363.putUnitDouble( idAngl, idAng, 0.000000 );
        var idDlt = charIDToTypeID( "Dlt " );
        desc363.putBoolean( idDlt, false );
        var idautoFill = stringIDToTypeID( "autoFill" );
        desc363.putBoolean( idautoFill, true );
        var idcropAspectRatioModeKey = stringIDToTypeID( "cropAspectRatioModeKey" );
        var idcropAspectRatioModeClass = stringIDToTypeID( "cropAspectRatioModeClass" );
        var idpureAspectRatio = stringIDToTypeID( "pureAspectRatio" );
        desc363.putEnumerated( idcropAspectRatioModeKey, idcropAspectRatioModeClass, idpureAspectRatio );
        var idCnsP = charIDToTypeID( "CnsP" );
        desc363.putBoolean( idCnsP, false );
    executeAction( idCrop, desc363, DialogModes.NO );    
    }