Can you force stun an enemy with Loda and then in the same turn use force push3 (replace turn) ?

As long as you still have the FP's, sure can. Only PUSH replaces attacks.

edit: My mistake, yeah, push replaces, stun does not, thanks Aaron.

No, Stun does not replace attacks. I'm thinking, Ray, that you meant to say 'Only Push replaces Turn." Any abilities that say 'useable on this character's turn' but do not say either 'replaces attacks' or 'replaces turn', then you can use those abilities at any time, regardless of what else you have done during that turn, so long as you don't interrupt any current actions (i.e. you cannot attack, then stun, then attack again, must resolve all attacks first).