The Commonwealth in its entirety was scrambling to find a replacement for the 6 pounder in order to keep up with German development, and several projects were started concurrently, such as the 8-pounder, 12-pounder, 75mm Vickers and 17 Pounder Projects. The Canadian contribution was the so-called “Canuck Gun”.
The gun was effectively a lengthened 6-pounder, stretched out from the earlier L/43 and L/50, to the L/63 length. Tests with the weapon showed a muzzle velocity of from 990 m/s with APCBC. Compare this with average of 792 m/s and 831 m/s for the L/43 and L/50 guns. Firing APCR the recorded penetration was 130mm at 30 degrees compared with the 100mm penetration of a L/43 shooting APCR with both shots at 400 yard.
Although the weapon was seen as an improvement and a success it was abandoned, as existing 6-pounder designs, firing the more advanced APDS ammo could achieve similar performance. I don't believe the weapon was ever tested for performance with APDS rounds. Although oddly enough the weapon was used as a testbed to test muzzle breaks for later marks of 6-pounders, firing APDS with high pressure casings (performance of that was never recorded as the weapon as a project was abandoned by that point.)
http://ftr-wot.blogspot.co.il/2013/04/commonwealth-uncommons.html
