There's a whole bunch of threads on it but no quick easy to access information on exactly how to apply for one.
Fill out this form and make a payment of $5 (if you're applying inland the payment is not necessary)
http://www.cic.gc.ca/english/department/atip/form-imm5563.asp
If you're requesting on behalf of your spouse you need to get them to fill in this form, scan and email it back to you.
http://www.cic.gc.ca/english/department/atip/form-imm5744.asp
Include: the completed ATIP form, receipt of payment (if applicable) and consent form (if applicable) in an email to: ATIP-AIPRP @ cic.gc.ca
Instructions on how to fill out the ATIP form can be found in other threads if you search.. for example, I ordered GCMS notes for my spouse who is outland. I ticked "Access to Information Act", then on the 3rd question "Email"
4th Question "No.. Consent Included"
next section "I am a Canadian Citizen etc.." then "Public" no need to include proof if you have a Canadian address.
Section C make sure you tick "electronic files" so as not to delay your processing while they photocopy your actual file.