Rally Poland is running 26-28 june. The closest rallies on WRC are Sardegna (4-7 jun) and Kenya (16-19 jul). I mean it's the most possible by my opinion and they said that tey want to get back as soon as possible. Estonia is pretty close after Kenya so I don't think that this could be replacement. Canada have few rallies next year scheduled. Croatia could mix up but I think that there is money issue. The remaining interested countires who want to host the rally on WRC calendar could seen this opportunity to jump in. India, Russia, Korea, Ireland...