DLASK is the only store I'm aware that makes canada legal 870 barrels in the short size for you to replace, they come stamped "DLASK ARMS" on the side with the length, chambering and other details. That makes it pretty easy to prove the barrel is legal and swapped, not chopped down. Lot of other barrels I've seen only state the caliber on them which leaves up the interpretation that the barrel was cut illegally and barrel marking lost in the process.
I had purchased a Churchill 12" temporarily while I was waiting for DLASK to restock. Sold it when i got the shorter barrel, they cost the same.