as many people know e-bikes can be pretty heavy. I'm looking for some help upgrading my cantilever brakes to v-brakes on my old mountain bike so it is better at stopping all of the weight added by the e-bike kit.
It should be an easy bolt-off, bolt-on upgrade.
Do note that old conventional brake levers aren't compatible with V-brakes. Some later model levers are. But it's usually required for a V-brake set up that you get V-brake levers.
Since your bike is now heavy, get the longest and strongest armed V-brakes you can afford. This will yield best leverage and less flex.
Also, monitor your rims for wear!! Keep the pads super clean.