As I said in a previous post. You are allowed to travel outside of Canada but must meet requirements to reenter:
"
If you are unable to return to Canada, we could determine that you abandoned your application. In that case, we will not process it. "
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=248&top=28
I have not seen people having problems but obviously don't go for more than 2 weeks because the inland requirement is to live in Canada.
Committing a crime while you're out of Canada is a good reason they will deny you, for example.
*edit* no one can guarantee 100% authorization because only citizens and PR are allowed.
I am going on vacation to Hawaii in June and am confident I'll be okay, but I'm also an American citizen