Here are some suggestions, by myself and others. See the sidebar for my offerings, not forgetting “Polar Bears Have Big Feet” for the toddlers in your life, so they don’t feel left out when older kids get polar bear books to read over the summer: Facts & Myths for middle school ages, and Outstanding Survivors and/or EATEN (the polar bear attack thriller) for teens and adults.
Titles from other authors that have a few mentions of polar bears amid great descriptions of life in the Arctic or Arctic exploration that would make good summer reading as well.
Freuchen, Peter. 1935. Arctic Adventure: My Life in the Frozen North, 2013 edition (original out of print). [about early 1900s explorations in Greenland] Echo Point Books & Media. https://www.amazon.com/Arctic-Adventure-Life-Frozen-North/dp/1626549990/
Freuchen, Dagmore. 1960. “Peter Freuchen’s Adventures in the Arctic” Julian Messner Inc., New York. [about early 1900s explorations in Greenland and Hudson Bay, compiled by his widow] https://www.amazon.com/Peter-Freuchens-adventures-Arctic-Freuchen/dp/B0007HYV5G
Sides, Hampton. 2014. In the Kingdom of Ice: The Grand and Terrible Polar Voyage of the USS Jeannette. Anchor Books, New York. https://www.amazon.com/Kingdom-Ice-Terrible-Voyage-Jeannette/dp/0307946916 Goodreads reviews here; National Geographic review here. Wikipedia summary of the expedition. ** I found this description of the late 1800s voyage into the Siberian Arctic fascinating but admit I skipped over the tedious bits of letters by De Long’s wife. In 2015, Russia planned to raise the wreck of the US Navy ship.
Treude, E. 2004. The work of Knud Rasmussen in the Canadian Arctic as described by RCMP Inspector Stuart Wood. Études/Inuit/Studies Volume 28, Numéro 2, 2004, p. 185–201. DOI 10.7202/013202ar https://www.erudit.org/fr/revues/etudinuit/2004-v28-n2-etudinuit1289/013202ar/ PDF here. [primarily about early 1900s explorations around Hudson Bay]