Well, it would still depend. What country are you going to be visiting? If you're visiting the U.S, you would (in theory) be able to request to return to Canada on your original single-entry visa. You can postpone the application, but the application itself wouldn't be what would cause an issue for you to come back.
People are generally advised not to leave the country during the application process in general for a number of reasons. Primarily because of the big "what if". Are you LIKELY to be denied entry on your second time entering the country? No, not if you went to a country like America and brought along documentation to prove your ties to your home country. But just because it isn't likely doesn't mean it will not happen. Anything could stop you, from stupid things like a computer glitch, or a border official having a bad day, to serious things like a criminal record, or not bringing a passport.
No one, not even a border agent or anyone working for the CIC can guarantee that you would be allowed to come back a second time. Simply because it's highly situational. The fact is that leaving Canada will mean taking that risk, and you'll need to weigh that risk against your reason for leaving. Most people will tell you to not take that risk, but if you chose to take it, have a backup plan in place and be prepared to apply for outland sponsorship instead.