Hi,
as per below url. Financial institution must provide this.I hope post office can also provide similar letter.
http://www.cic.gc.ca/english/resources/tools/perm/express/intake-complete.asp
Document requirements
The applicant should provide an official letter(s) from one or more financial institutions that lists all current bank and investment accounts as well as outstanding debts, such as credit card debts and loans.
o The letter(s) must be printed on the letterhead of the financial institution and must include the applicant’s name, the contact information of the financial institution (address, telephone number and email address), the account numbers, the date each account was opened and the current balance of each account as well as the average balance for the past six months.
Other documents may also be requested, as necessary.