+1(514) 937-9445 or Toll-free (Canada & US) +1 (888) 947-9445
There's no format. Just think of it as writing a business letter and explain what you need to explain.
 
You can address it to IRCC, then state Subject , Address as Sir/Madam, Explain your points of additional information under each section. Closure of Letter. That's it.