Heard of X2Y components? Basically a balanced capacitor network designed to reduce EMI. Heavily used in the automotive sector for suppressing brush noise. Works better than three caps, and will be a snap to install in a motor like that.
You can get them from Digikey.
Have a look at this for information about how they work and how to fit them- http://www.johansondielectrics.com/imag ... Basics.pdf
Three caps should also be fine wired as close to the can as possible. Inside the can would be best and looks tidy, but more tricky to install. SMD caps are very small 1206 components are easy to solder with conventional sized soldering kit.