the FIRST thing to consider is brake pad toe-in. the pads might be less noisy if you angle the pad so the front hits the rim first, then flattens out. this is tricky to do with canti brakes
the last time I owned a bike with canti brakes, the brakes sucked and were noisy to boot. my experience that helped a lot was:
1. mount the cable stop at the
fork crown instead of top of the head tube. that make the shuddering go away. $15 fix.
2. angle the pads with a toe-in bias. this made most of the squeal go away
3. replace the short "road" pads with some longer, curved "mtb" pads. these made the brakes work 100x better. I went from "slow down" at full effort to "lock up both wheels" with one finger gently pulling the lever. it that's too much brake for you, you can get more modulation with a more aggressive toe-in angle.
all that worked for me. YMMV.