Generally the fastest way to apply is outland - thankfully your boyfriend can stay in Canada during this time.
You need to be married first before you can sponsor. Are you getting married in Canada? My husband came with a one way ticket. He explained he was visiting his girlfriend and he hadn't decided exactly when to leave. The border agents can give you 6 months in this country, but if they suspect that you may stay longer, they may request you leave in a shorter amount of time. They rarely will deny entry, but if they believe that you are not going to leave the country when your status expires, they could. My husband was given 6 months. Once you are in, you can apply for an extension here: http://www.cic.gc.ca/english/visit/extend/visa.asp
Thankfully, sponsoring an American is pretty simple as marriage fraud is very rare with that country. But ensure you have proof that you have a genuine relationship. My husband is American and the proof we showed was tickets to all the times he's visited, receipts for all gifts, pictures of us together before, during and after the wedding, joint bank accounts, joint utilities, joint leases, having him as a beneficiary, etc. You honestly can never be too careful.
Here is the application page. Read all of it carefully. There are guides that show how to fill it out. http://www.cic.gc.ca/english/information/applications/fc.asp
We sent in EVERY part of the application. Pages that didn't apply to us (use of representative, dependents, etc) we just wrote a line through and wrote N/A, just so our application was complete. You don't have to do this.
Pay your fees, then send off.
Currently the wait time for the United States (assuming Ottawa is the processing centre) is about 15 months, so expect to have to extend your boyfriends stay possibly more than once. That time doesn't guarantee that it will be exactly 15 months. When we applied it was 14 months and we were finished in 7 months.
I hope this makes sense.
Just read read read and don't be afraid to ask.