To sell?
I hope you have a great new idea, because there are a number of very good suppressor manufacturers out there (Gemtech, AAC, Knights, AWC, John Tibbets, Sound Tech, SWR, Tac-Ord, SRT Arms, etc.) so the competition is quite high and with that much competition the profit margins aren't. Many people in the suppressor market will not flinch at the price of a premium Gemtech or Knights can, but a large part of the lower end market is very price sensitive.
To get the manufacturing license you'll need to apply for an 07 FFL and pay the SOT ($500/year, reduced rate). You'll also need to pay the ITAR fee for the State Dept. ($1750/year). Obviously you'll also need a properly zoned facility for industrial or light industrial applications (BATF will check this) and all other applicable state and local business licenses. If you're going to sell suppressors or any item you manufacture, I'd also highly recommend good liability insurance.
If you just want to make a can for your own use and not for sale, get a Form 1 (in duplicate with two completed FBI fingerprint cards, $200 tax, and US citizenship certification, etc.) and send it all in. Once approved you can make your own can. As the original manufacturer you can repair and replace parts on your can, but you cannot have spare parts on hand (like neoprene wipes).