One should always be cautious. Talk to the locals from where your hike starts. If a polar bear has recently been spotted, they would know. It is unlikely that you will see a polar bear but chances of encountering polar bears are more likely in the remote places of north and/or east Greenland. For summer hikers: there will still be ice floes coming from the North Pole, and polar bears tend to travel along the coast line following these.
2. Destination East Greenland does rent out rifles. Contact them here.
3. Final Guidelines for encounters with polar bears from the Ministry of Fisheries, Hunting and Agriculture
4. Guide infographic: Encountering Polar Bears While Hiking in Greenland