Take said crankarm(s) and flip them on their side so the pedal touches the ground (You can do both at the same time if need be if you have crank pullers.) Then, apply quite a bit of liquid wrench or a similar product to the area where pedal meets crank, lightly tapping the crank arm every so often to let the oily stuff sneak in farther. Let it sit for at least an hour And give it another go with a dedicated pedal wrench. I've dealt with my share of stuck pedals, and they almost always royally suck.