Hi
Check here:
http://www.cic.gc.ca/english/information/applications/fc.aspAs common law partners you will need to provide evidence of cohabitation for 12+ months, continuous. Evidence of combining your affairs; joint bank account, lease etc and various other bits and pieces.
The guides for sponsor and applicant should be read very closely.
When you've done that, come and join us on the family class thread! You'll find lots of answers to questions you may have that have already been asked and if not, you can ask and someone very knowledgeable will answer. Posts by rjessome, PMM and ariell plus a few others are usually spot on!
Also, the UK citizen will need a medical - around £250 - £300, a police certificate from UK - £35 (ensure a clean record INCLUDING DWI/DUI or if not look up rehabilitation rules), plus he will need police certificates from any other country he has lived for, I believe, more than 6 months. The application itself will cost around £600/$1040 (assuming £1 = $1.75).