No matter what I would do, I don't think I'd stand a chance against a polar bear.
They are four and a half feet taller than me, and several times my mass. They have claws like razors and teeth like daggers. They are also many times stronger than even the strongest humans. No matter how much time I spent in a gym working out and honing my skills, I would always lose without a weapon.
Even with a good gun, a polar bear might be able to get me. They are quick on top of everything else, and might be able to rip my throat out before I can gun one down.
I think my best strategy would be to just avoid their habitat. Hopefully they stay in the far north, but I hear they are straying further south these days.