I'm an example of what your looking for. I'm the Canadian citizen, married to an American, living in the USA.
What I had to do was prove intent to reside in Canada. It's the thing you want to focus on, even after your application is submitted. Since this is such an ambiguous request, we initially sent in communication with a realtor, some quotes for moving expenses and a few emails from me and some schools.
For proof of marriage, I showed our bank accounts and my bank allows us to narrow down 12 months of deposits only and I printed all the deposits. This way I demonstrated he made the money and it was deposited into our joint account. Plus, I showed all our savings account, stocks, 401K's, his life insurance policies, and the beneficiaries on them were left to each other and 6 pics of us. This was our demonstration that we were married (along with our marriage certificate). We've been married awhile (7.5 yrs) like you, and we have a son together.
When the sponsorship was approved, I then went on to gain more evidence of proof to reside in Canada upon approval. Thats when I bombarded Ottawa's email every time more concrete proof was established. Some examples of what I submitted was proof we paid off our 2012 and 2015 cars and obtained the lien releases. This is pretty good proof since we can export the cars out of the USA and import the cars into Canada (it's hard to export a car with a loan). My husband also submitted his resume to several tech companies, which many responded and I showed all their correspondence in their emails. I showed interviews being setup, and the communications before and past the interview stage. This is the one area I stress to anyone living outside of Canada with their spouse. FOCUS on the proof of intent to reside, and email everything that you gather after the application is gone (the email addy of your VO will be in the SA email). One thing to note, when you do this, give an explanation of why it's proof and then make sure you send only one PDF under 5 MB.
If you look in the spreadsheets, those who are residing exclusively outside of Canada (like us), 9 times out of 10 get a document request for additional proof of intent to reside in Canada. This request can slow your app down by 1, or many months.
Once your spouse receives SA, I recommend about a month later ordering the GCMS notes, every month. Just to assure everything is and has been attached to your file. If you see deficiencies, like a police report wasn't attached etc, you can focus on rectifying this before you receive a document request. Sadly, there have many documents misplaced at either Mississauga or the VO.
Good luck!
