Not sure which bolt is frozen, but if it's one holding on the caliper you should be able to use the soak in penetrating oil and breaker bar technique. I have never snapped anything over 17mm. I have an 18 inch long 1/2 breaker bar. Have not come accross anything I can't free. Try the penetrating oil technique, it does work, and with a good breaker bar should be no problem. Siz sided socket good idea.
As a last ditch effort you could always cut the head off with a cutting tool (dremel) and then trhead out the stud. Drill out as absolute last ditch effort.
Good luck, be patient,