For all the faults one can find with “Grand Isle” (2020), I am stunned the accents aren’t one of them. Sure, Nicolas Cage puts forth the usual half-hearted effort in the latest product from his B-movie assembly line, and the story (strange couple exposes hard-luck handyman to a deadly secret as hurricane pounds Gulf Coast) is a continuity-deprived head-scratcher. But co-stars KaDee Strickland (Cage’s wife) and Kelsey Grammer (murder investigator) consistently conjure a couple of the best Cajun accents I’ve heard in a while. For all the times you had wished Frasier would just shut up, this is not one.