Are Canik and Walther Magazines interchangeable?
"Since the Canik TP9SF magazine is identical to the Walther PPQ m2 9mm mags and can be fired without any issues and are 100% interchangeable then your extensions should work on either. Am I correct?"
No. While Canik mags may function in a PPQ, the Canik mag is slightly narrower. As a result, the basepads are NOT interchangeable.
HOWEVER: The new Walther PPD full-size (emphasis on full-size) uses an 18-round mag tube that is nearly identical to the Canik (the mag catch notch is slightly deeper). You could use that magazine with a Canik extension on it in a PPQ -- but not a PPD!
Why? The PPD frame has a pronounced "tail" that comes down below the end of the mag tube. If you try to use a Canik basepad on the PPD, the bulge on the back of the mag (that houses the screw) will hit the "tail" of the PPD frame.
To fix that, we made PPQ-style +4 basepads for the PPD (with the flat plate on the back).
The PPD +4 basepad will fit on a PPD/Canik mag tube, and THAT combo can be used in a Walther PPQ, Walther PPD (either size), or a Canik (all three sizes).
If you add magwells to this discussion, things get even more complex.