Black throated blue warbler.
Black throated blue warbler, Rondeau Provincial Park, Ontario, Canada, May 8, 2017.
Unlike other warblers that molt into "confusing fall plumage," male Black-throated Blue Warblers keep their distinctive black-and-blue plumage year-round. The distinctive white square on the wing also helps ID females.
source - https://www.allaboutbirds.org/guide/Black-throated_Blue_Warbler