There aren’t any specific formats in which this letter has to be written, but there are specific details that MUST be provided in these letters.
This includes the following list of information for the person expected to travel:
°Full Name
°Birth Date
°Address
°Phone Number
°Purpose Of This Visit
°How Long Planned To Stay
°Where Person Will Stay
°When Person Plans To Leave
Also specify how this person will pay for expenses while visiting Canada.