hello FT!

I'm flying from FLL-ATL-YYZ and I'm not sure if I clear customs in ATL or YYz? If I do clear customs in ATL, will I have to recollect my baggage and check it again?

I have the same question for my return (YYZ-MEM-FLL)

Thanks in advance for your help: Im a novice flyer and this is my first solo trip.