Amanda Tidmarsh, 52, from Brynna, was walking her two rescue dogs along the beach in Ogmore-on-Sea when she noticed the bottle mixed up with seaweed.
She said she was "so excited" to find it, having previously joked with her family that she was "always on the hunt for treasure".
She is waiting to hear back from the crab fisherman who threw it overboard.
Canada is more than 3,000 miles (4,800km) from Wales, and the co-ordinates written on the letter show it was thrown in the sea nearby in November 2020.
