I had the same question but found an example after searching a bit on the internet (http://www.canada-city.ca/canada-immigration/posting.php?messageid=8707
). Essentially, you write a letter that has the same standard phrases and a similar layout as the "Statutory Declaration of Common-Law Union" (IMM5409E) but of course you change the middle part. Your ex does not need to be involved! Then it needs to be certified by a commissioner of oaths. We just went to the town hall (in Montreal, actually the one for our borough) where the receptionist could do it for us after paying $5. But others may do it too.
Here it is -- strategic places marked with (); hope that helps.
STATUTORY DECLARATION OF SEVERANCE OF COMMON-LAW RELATIONSHIP
In the matter of an application made pursuant to the Immigration and Refugee Protection Act and Regulations and in the matter of common-law union, I, (name), of the city of (city), in the province of (province), do solemnly declare that:
1.The common-law relationship between myself and (name) ended on (date).
2.At no time since our relationship ended have we lived together, nor tried to reconcile the relationship.
3.This declaration is made with the knowledge that it is being relied upon by Immigration Canada and the Canadian Embassy in (city), (country).
I make this solemn declaration conscientiously believing it to be true, and knowing that it is of the same force and effect as if made under oath.
Name of Declarant: Signature of Declarant:
Name of Commissioner of Oaths: Signature of Commissioner of Oaths:
Declared before me at the city of (city), in the province of (province), this (number)th day of (month) of the year (year).