cedarjet said:
The fastest way is to stay 4 years without leaving a single day, then applying.
The fastest way is through the fast-track process available to members of the CAF.
"The fast-track provision will accelerate citizenship for permanent residents serving in the CAF and foreign military members on exchange with the CAF.
Those who have served for one year less than the standard residence requirement for citizenship may qualify for a grant of citizenship, provided they meet all other requirements. This means the length of time you served in the Canadian Armed Forces is used instead of the length of time you lived in Canada." Source: http://www.cic.gc.ca/english/citizenship/become-eligibility-armed-forces.asp
But otherwise (for non-members of the CAF), yes. The fastest way for a PR who has not and does not serve the CAF is to not leave the country until becoming eligible to apply.