A question about Illusion creatures?

"The effect on an illusion creature says that the creature will be sacrificed if a spell or ability targets it. If i redirect or cancel the spell targeting it, will it still be destroyed?"

Yes. The Trigger for that ability is When the creature is targetted, which occurs as soon as the spell or ability which targets the creature goes on the Stack. As such, the ability to sac the illusion creature will already be on the Stack before you get priority to be able to Cancel/Redirect/etc the targetting spell/ability.

"Also, can a card like Cancel or Rewind counter a creatures being summoned and a creature ability?"

Creature being summoned: Yes, so long as the counterspell doesn't have some extra restriction, such as on Negate. A creature's ability: No. That requires something that specifically says it can counter an ability, such as Stifle or Voidslime.

Unfortunately, what will happen is the sacrifice will still happen.

That's because that's a separate trigger which happens as soon as the spell is played and a target is announced. It can be countered with Stifle, though in most cases that won't help.

Unless...it's a creature spell, which has a ETB trigger, in which case that shouldn't be announced until it actually happens.