I used to work for one of the largest producers of canned corned beef in Argentina, so I am glad to provide an answer.

The process starts when the beef is cooked in a continuous cooker. The goal of this is obtaining the broth, which is then evaporated in order to obtain meat extract, a very valuable product. The cooked beef that remains is then cleaned of connective and fatty tissues, mixed with curing salts and coarsely minced. This mix is then canned and sterilized in autoclave.

So, as you see, the main difference with homemade stuff is that you cook the meat before adding the curing salts. This is done because you cannot add the curing salts before cooking if you want to obtain meat extract.

Canned corned beef usually does not contain spices.