Wanda/Thor
I trust her too. I do not believe Steve does...he does not like that I work at SWORD.
He is one of the most intelligent beings in his universe, and knowledge is dangerous when misused. I do not doubt that he could activate the Tesseract in an adverse way, even if accidentally, or do something that possibly reverses everything and sends everyone home at once, even those who do not wish to go. I do not recommend allowing him near it.