Having done a fair amount of research on this topic for clients and having talked to all the major suppliers, here are my thoughts:

(1) Entrée Destinations is one of the top DMCs in Canada and would be my 1st recommendation for a tailor-made luxury tour if there are no budget concerns

(2) Natural Habitat Adventures, a partner of the National Geographic Society, offers some excellent 6-7 day tours with a strong emphasis on education, ecology etc. (while "nice", don't expect "luxury")
https://www.nathab.com/polar-bear-to...SAAEgIA9vD_BwE

(3) If you just want to tick that adventure off your bucket list without spending a week or longer up in Churchill, Classic Canadian Tours arranges several charter flights / day tours each year:
Classic Canadian Tours - Polar Bear Safari - Our Tours

Additionally, there are several lodges in the area that offer various half day / full day tours.