That Miyata is really nice and pretty well
preserved. Before you go about replacing anything related to the brakes, I would read up on setting up cantilever brakes. Enjoy that endeavor. If the levers smoothly close the brakes and the brakes smoothly return the levers, then the cables and housing are fine (lube can come later). Focus on set up. If your finger nail can depress the brake pad, don’t replace them yet. If they are hard plastic dense, first file them to investigate if the hardness is only skin deep. I bet they will work adequately without anything but fine tuning. Not just advising ways to save $$$$ but suggesting that getting those brakes working well first and then making improvements incrementally is (for me) part of the fun of learning.