As you seem to have realised, the chances of the Canadian immigration authorities finding out about your caution are probably zero.
However, the 'official' answer to your question is that you must wait until 5 years after the date on which you committed fraud and then apply for rehabilitation (for which you have to pay a C$200 fee). Quote:
"You are eligible to apply for rehabilitation if you have committed a criminal act outside of Canada (for which you were not charged) and five years have passed since the act".
Source:
http://www.cic.gc.ca/english/visit/faq-inadmis sibility.asp
As I read the information on the Canadian Immigration website, the rules regarding 'inadmissibility' and 'rehabilitation' are common to all people seeking entry to Canada. (i.e. you're inadmissible to enter, even as a tourist, for a period of 5 years. Thereafter, you can seek rehabilitation and you'll then be eligible to seek any type of visa for which you would have been eligible if you'd not committed an offence);
http://www.cic.gc.ca/english/visit/apply-who.a sp
If you 'forgot' about your brush with the law, for the purposes of tourist travel, it could present a problem with a later application for a visa (on which you declared your conviction) because, by not mentioning your caution, you'd effectively be committing fraud again.
Chris