I'm from the states and came in Oct '09 and was married in Dec. As a US citizen, you have 6 months to stay unless there is a specific date written in your passport by the IO. We applied for PR in March and around the same time filled out an extension request (TRV). You can find the forms on this page: http://www.cic.gc.ca/english/information/applications/visitor.asp
You need to file this at least 30 days before your time expires (5 months from the date stamped in your passport) For the TRV we sent proof of applying for PR (fee reciepts, copy of sponsorship agreement) and we included a letter, signed by both of us, that said that my husband would be responsible for me finacially for the time I stay in Canada and that I would leave before the visa expired. In the "reason for visit" question, I put that I wanted to stay in Canada with my husband during the PR process but would leave if an interview was requested or if I was asked to leave due to visa. It took about 2 months to get a reply back and the IO gave me a full year. If you don't get a reply back after your 6 months is expired and you filled out an extension, your considered implied status until you hear back from the IO about your status. I've read many times on this forum from people that if you have proof of PR there is a very good chance you'll get to stay 6 more months (or if they're nice they'll give you a year.
) Hope this helps.