get a drift punch that will fit in the bolt hole and get the case squared up on a solid bench andI blocked so the bearing can come out. The impeller is going to be junk once removed more than likely.  Carefully wail it with a good big hammer. it will come out. I have seen a lot of frozen ones like this, you can heat the impeller with a torch but that will be guaranteed to ruin it.  just need a good hard hit and the shock to get it moving. a press could send stuff flying and the shock is what you need to get it started.