I posted a brief summary of possible medieval Norse (Icelandic-Greenlandic) polar bear catching before in: How did medieval people capture and transport dangerous animals while keeping them alive?, but I'm rather negative in regarding it as any large-scale domesticating attempt of the bear as the specie since the lawbook (cited in the linked post) primarily applies the relevant rules originally for dogs to the tamed polar bear, not treats the latter as a sub-specie of the pet bear.

12th century Icelandic penitentiary also mentions the (polar) bear trap, so they were probably primarily caught by the trap if it was necessarily.