Can I play vi peacekeeper in reaction to a temporal breach which targeted brynhir?

It depends on whether Brynhir's "When you play me" trigger has already resolved — and whose side you're on.

If you're an opponent of Brynhir's controller and her trigger already resolved this turn: No. "Opponents can't play cards this turn" is a blanket prohibition — it doesn't just restrict timing, it forbids playing any card at all. Vi's Ambush gives her [Reaction] timing permission, but that can't override a "can't play cards" effect (FAQ 7114: even Hidden cards are blocked).

If Brynhir's trigger is still on the chain (unresolved), or if you're Brynhir's controller (her ability only hits opponents): Yes. Temporal Breach on the chain creates a Closed State, and Vi's Ambush lets you play her as a Reaction to a battlefield you control where you have units (Rule 813.3.a). Note this doesn't stop Temporal Breach — it resolves, banishing and replaying Brynhir, which re-triggers her "When you play me," so the lockout still lands afterward.