Mix 1 cup orange juice and the lime juice; pour over pork roast in non-reactive
bowl. Cover and refrigerate, turning pork occasionally, at least 4 hours.
Remove pork from juice, reserving juice. Pat pork dry. Mix garlic, oregano and
pepper; rub evenly over pork. Place onion, celery and carrot in shallow roasting
pan; sprinkle with salt. Pour reserved juice over vegetables. Place pork on top
of vegetables. Insert meat thermometer so tip is in center of thickest part of pork
and does not rest in fat. Roast uncovered at 325 degrees F, spooning juices over
pork occasionally, until thermometer registers 170 degrees F, about 2 1/2 hours.
Remove pork; cover with aluminum foil and let stand 15 to 20 minutes before carving.
Place vegetable mixture and 1/2 cup orange juice in blender container. Cover and
blend on medium-high speed, stopping blender occasionally to scrape sides, until
well blended, about 1 minute. Heat to boiling.