You would not have a friend fill out "STATUTORY DECLARATION OF COMMON-LAW UNION" form. That is for you and your common-law partner to fill out together.
I think you're referring to statutory declarations from friends and family that are aware of your relationship. There is no form for this, you will have to have them write a letter saying they know you're in a common-law relationship and that the relationship is genuine. It should include details about how they know you and your spouse, how you met, why they can say you're in a genuine relationship, etc. There is no standardized format and it can be written in a letter format about a page or so long. A lot of mine were "from the heart" and included some details about how my family has witnessed our loving relationship through the years and stuff like that. I also had my spouse's parents mention that they helped us move in together and pick out furniture, further verifying the date we began the countdown to common-law. You can talk about holidays they spent with you two as a couple. This can be written in any language but should be translated for CIC and notarized.
