I had a lawyer and included what she suggested, which was that we each wrote a letter describing how our relationship developed, got letters from friends and family attesting to the genuineness of our relationship and explaining how they knew, various photos (all with the date and people in the photo written on the back), and proof that we were each other's beneficiary for RRSPs, insurance, etc. This did the trick and we did not need to interview.
There's been quite a lot of discussion on this topic in the past, so if you need more information, try a search and you should be able to find more comments.