Numerous Canadians have traveled abroad with a criminal record and have not experienced any trouble resulting from their record(s). Unfortunately, this can often lead to a false sense of security regarding the risk of traveling with a criminal record. Virtually all countries of the world have various laws prohibiting or discouraging entry with a criminal history, with certain exceptions made for certain offences.
Outside of the United States, no other countries have negotiated access to CPIC, Canada's federally managed criminal record repository. For this reason, these countries do not typically take an interest in checking on short term visitors. The process to check on visitors through their embassy being rather burdensome. As a rule of thumb, if a traveler is entering the country for less than a month, they will not have their background checked.
However, in those rare cases that a traveler is checked, the consequences of having a record can be devastating, often way beyond what one would expect for simply traveling with, say, a 20+ year old criminal record.
Take the case of a recent unfortunate Canadian man from Maple Ridge, British Columbia. On an all inclusive vacation to Mexico in early 2008, he was involved in a minor altercation in a Mexican night club frequented by both tourists and locals. After the Mexican police looked into the man's file in Canada, and found a criminal history, he was arrested and detained, pending an investigation. Despite his innocence of any crime (at least not serious), he remains in Mexican prison to this day, having yet to even appear before a judge. His family is desperately trying to free him, but in the mean time, they pay several hundred dollars a month just to keep him alive. Such is the fate of numerous Canadians and other foreigners in many South American countries, where the support payments are coveted. People with criminal records are often the subject of discrimination here in Canada, but when overseas, the problem and consequence is multiplied many fold.
Considering the risk, it is always advisable to clear your criminal record with a Pardon before any foreign trip.