There is one intresting factor nowaday's that may decide the outcome of such a fight; polar bear's, today, no longer reach the enormous sizes they used to, as a result of the scarcity of prey in their habitat's., this being an effect of global warming.
The average polar bear is usualy more slender and longer. While kodiak bear's are bulkier and'thus heavier when fully mature. It would be a very even match. Since both have similar advantadges and dissadvantadges. But having the key advantadge of weight, my guess would be for the kodiak.