It sounds as if you are not yet in Canada and have not been given PR. According to the following, I don't think you can write an invitation letter until you are settled in Canada. Here is a section of the link, but read the whole thing online. Good Luck.http://www.cic.gc.ca/english/visit/letter.asp
Your letter must include the following information about the person being invited:
•Date of birth.
•The person's address and telephone number.
•Your relationship to the person being invited.
•The purpose of the trip.
•How long the person you are inviting intends to stay in Canada.
•Details on accommodation and living expenses.
•The date the person you are inviting intends to leave Canada.
Your letter must also include the following information about yourself:
•Date of birth.
•Address and telephone number in Canada.
•Whether you are a Canadian citizen or Permanent Resident
•A photocopy of a document proving your status in Canada. For instance, a Canadian birth certificate if you were born in Canada or a Canadian citizenship card if you are a naturalized citizen. If you are Permanent Resident, you must send proof of your permanent resident status (a copy of your PR card or your IMM 1000 proof of landing).
•Details of your family unit, including names and dates of birth of your spouse and dependants (this is mandatory for the Parent and Grandparent Super Visa);
•Total number of people residing in your household, including those you have previously sponsored and whose sponsorship is still in effect (this is mandatory for the Parent and Grandparent Super Visa); and
•A written and signed promise of your financial support for your parents or grandparents for the entire duration of their stay in Canada. Proof of income at a level meeting or exceeding the low-income cut-off (LICO) for the total number of people, including the visiting parents or grandparents, must be included (this only applies to the Parent and Grandparent Super Visa).
See a complete list of countries and territories whose citizens require a Temporary Resident Visa to enter Canada.