sorry to add to the confusion on nbi remarks, but i got this info from the US visa requirements regarding NBI.
NBI CLEARANCE: Applicants aged 16 years and older must have a valid Record Clearance for Travel Abroad Purposes from the National Bureau of Investigation (NBI). Clearances should be in the applicant's current name, birth certificate name, maiden name, married name, and any aliases or nicknames ever used, including different spellings of all names ever used. An official letter of explanation from the NBI is required for any notation of “No criminal record”, "No pending criminal case” or “With derogatory record.” For immigration purposes, an NBI clearance is considered valid only for one year from the date it is issued.
am not an expert on this and it would be great to hear from the seniors.
hopefully, an explanation letter of not commiting any crime would be sufficient. here's the link that might give u an idea and help u prepare
http://www.canadavisa.com/canada-immigration-discussion-board/-t39358.0.html