Todd said he was thrilled to be picked and feels his horses are in good shape.
''I am very happy with my horses at the moment and the strong team that has been named," he said.
For Johnstone, who was forced to drop out of contention leading into the London Games when his horse was injured, is delighted.
"To go to Rio and try to win a medal for New Zealand has been my No 1 focus for the last four years, so to be one step closer again is really, really exciting. I can't wait," he said.
Brougham will become the third New Zealander to compete in an Olympic dressage programme, after Kallista Field at Sydney in 2000 and Louisa Hill at Athens in 2004 and London four years ago.
Brougham set off for Europe in March to finalise her buildup.
"I am very much looking forward to being part of the New Zealand team at Rio," she said.
"Now we can focus 100% on the preparation and training for the games."