PHD (post hole digger) with auger bit little bit bigger than hole you need. so if hole is a little bit off angle. things can be set straight. and back filled around.
get the optional "down force kit" for many PHDs. that is a hyd cylinder to help push auger into the ground. sod may be easy, but there is a chance you will hit hard ground some place.
you could do a "foam marker" get a cheap 12v spray tank, you could toss into the FEL of tractor. and then using some lumber and some straps to fasten lumber to FEL bucket. and then run a hose from tank in fel to driver seat, and cheap valve or modified spray gun. that has a hose that goes back to fel and down the board. to leave a "marker of foam" when ever you set PHD down, hit the foam marker. for a couple seconds to make foam drop for the next line of trees. the first line you make for trees will be critical in getting straight and spaced correctly. but *shrugs* and would most likely be a 2 person job. one on tractor. and a spotter. just to make sure auger bit is straight and double checking driver in keeping things straight.
get all holes dug, and if you see a hole off after doing the entire field. you can go back and mark it or dig it with a shovel to meet specs of x,y coordinates.
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once all holes are dug, drive the truck / trailer down in between the holes. setting the trees in holes. and back filling.
having bare roots, the PHD will act like a tiller, and chew up the dirt into little chunks, making it easier to sprinkle the dirt in and around roots. vs large chunks of dirt. and i would think make for easier slight compaction around each tree. other words think about how you want the dirt around each root bulb. do you want hard compact large chunks of dirt. or kinda of a fluffly dirt that soaks the water in?
i am a tad against excavator or backhoe. due to bucket, will result in large size dirt clods. and be a pain in rear to bust clods up, and back fill around trees. if you were removing stumps ya excavator or backhoe. but for planting. i don't know about that.
a tree spade could work. that you see many nursery trucks and you can get them as 3pt hitch. but i tend to see them for larger size trees that are not grown in pots. were they come out put tree spade down into the ground. and it pulls out a hole in the ground. and then they set the large size tree down into hole.
also planting that many trees, most likely means need to replant some of them. a PHD would come in hand for that.
honestly a PHD and doing fence lines, once ya get going goes pretty quick. trees are not like seed crops (corn, beans, etc...) were millions of seeds are put in.
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double check what type of harvesting equipment they use and how critical it is to be on X,Y grid. that may make a huge difference. it may mean difference of getting heavy duty string, and stakes to make a grid. vs rough placing things and marking as you go.
also double check "mower" they use. to figure out min spacing and max spacing that could be had.
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if ya go with the tree planter for small saplings that others have shown. you could possibly modify a potato hiller, or rather make that a disc. along with modify a potato plow / ripper. and modify it all together for something. if you want a wheel that marks distance between trees. instead of a marker on tractor tire.... and you use tires to bring dirt back around saplings and compact it some. find tires/rims that are perfect size in circumference. for 1, 2 or 3 revolutions of the tire. and just paint a mark on side of tire. to reset wheel. just lift up the 3pt hitch tree planter, spin wheel, set 3pt hitch back down. and take off down the next line. and for backup, just drag a chain or like further away and off to the side. to double check you did not miss count revolutions/mark on the tire. as they guy putting the trees down into the hole.
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other thing to think about, if irrigation lines will be installed or if, a water tank on trailer will be used.
if irrigation lines will be installed. i would imagine only so many trees can be water at one time. how and were would the irrigation lines be installed? will they be just tossed onto the ground for first couple years? and then rolled back up? or permanently installed and if permanently i would assume, wanting irrigation lines away from tree roots and down the center line between the lines of trees. and teeing off to each tree.
while it may be just your job to plant the trees. what is the overall plan/ goal to get things done?
) to collect excavated soil if you need to. I would guess a good worker with a round-nose shovel could dig at least fifteen an hour in sod (should be able to do more than that!); that's two days work for two guys (plus planting). 
