You are right, it would make more sense that "Proof of intent to move back" would be done in Canada, but local visa offices abroad are like small parts of Canada. It is still officers who are employed by the Canadian Government who would process your application
It is not easy to prove this, but sit down with your spouse and brainstorm. Have you discussed this with your family, friends, even your spouse IN WRITING? If so, submit some e-mails, text messages, letters etc. that show this as a part of conversation. If you haven't already done so, start looking at jobs and places to live. You may want to contact them by e-mail to send a resume and inquire about possible future employment and contact realtors if buying property or rental offices if renting. Also, contact a bank to inquire about opening accounts for you and your spouse, ask them what is required for, let's say, a joint account and how to go about it. Print your correspondence and show this as proof as well.... and anything else you can think of....the more the better!
Before SA, they mostly look at eligibility (your status, whether you have any debts to the government, if you are on social assistance, if you have ever been convicted, if you declared bankruptcy, if you've ever been detained etc). After AOR2, it is the applicant's turn for a thorough background check once they start processing.