While a good sponsorship letter is key to laying out your relationship in an easy-to-read format for immigration officials, you should also consider having friends or family write letters of support attesting to your relationship together. For example, if any of them attended your wedding and has visited you on occasion they would be great candidates to put together a letter of support.
While it doesn’t have to be quite as structured as the sponsorship letter it should mention dates especially the wedding date and give details about the wedding as well as details on any further contact the family member or friend has had with both the sponsor and principal applicant. It should serve to backup the facts given in the sponsorship letter. Think of it as a supporting character with the lead actor being the sponsorship letter.
Finally, there obviously can be more than 1 support letter from family or friends but do not go overboard. Submit 2 or 3 letters at the most and choose wisely who to ask to send one so that they complement each other in supporting your relationship.
Don’t waste IRCC’s time with overlapping and trivial detail. Get the essence of the relationship and main facts and that will help significantly.