CC2 and CC11 are functionally the same. They can be used to send a control change messages from 0-127. What they are assigned to control determines what they do.

CC2 is by default assigned to Breath Control.
CC11 is by default assigned to Expression.

Perhaps your question was really what is the difference between CC7 (Volume) and CC1 (Expression). Here is a short article by Sweetwater than explains the difference.

https://www.sweetwater.com/insync/what-difference-between-midi-volume-expression/

Perhaps your question was really what is the difference between CC7 (Volume) and CC1 (Expression).

Perhaps you meant what's the difference between CC7 (channel volume) and CC11 (expression).
CC1 is the Mod wheel.

Ultimately, I am wondering how I can use my TEC Breath Controller to play the instruments from my VSampler and Kontakt samplers on an instrument which have NOT already been designed to properly work with Breath control.
The Sample Modeling instruments seem to filter out the "keyboard note on velocity parameter" as it pertains to velocity layer zone (so of course the loudness/brightness can be determined by the Breath controller, as opposed to the velocity of the physical key press).
So maybe I need a midi filter/merge software to in effect replace the "note on velocity" with a velocity determined by the Breath controller, so the Breath controller controls both "note on velocity" AND "expression level during the sustained note".
(Kontakt scripting of course could accomplish this, but I need to find a tutorial on this specific subject)

There must be a good article on this subject somewhere. 🙂