I wrote 2 letters in total.
The first is the main invitation letter with a heading "Invitation Letter to My Mother" and addressing my mom. It has 2 pages. First page starts with my intention, little background of my mom and myself (with emotional touch), my current Canadian status & family size, financial condition of both my mother & myself, my plan when my mother comes to Canada and finally ending it with request for approval. The second page (back) contains my info (as an inviter) and my mother's info (as an invitee) like it's stated in the CIC format.
My second one is a short 1-page letter with a heading "Declaration of Support". Here I wrote in affidavit style who I am, what I do, where I reside, what my Canadian status is, what my mom does, where she resides, why she is coming here etc. It's short summary of everything I wrote in the invitation letter. But I made it look like a cover page for all my financial docs as the heading is meant for.
Both letters were notarized here in Canada.