In assessing the relationship, they will look at elements such as age difference (if any), religion, nationality/language, education, economic factors, and more. On this forum we commonly refer to these as red flags. Many people have red flags and still have successful applications. However if there are two many red flags this can create concerns it's a marriage of convenience on the part of the applicant. If you have a number of red flags this is something the applicant should be prepared to address this if asked in the interview. For example, if you don't speak each other's language fluently, you should be prepared to explain how you communicate. If you are from different religions, you should be able to explain how you have addressed this together as a couple. Etc.
In your interview, I think the applicant should be prepared for extensive questions around the fact that you haven't met in person and how you have been able to establish a strong and conjugal relationship despite this. IRCC will want to understand why you should be regarded as a conjugal couple rather than two people who are just dating. So this is what I would prepare for if I was in your shoes. It would be a good idea to spend time looking at the conjugal definition and requirements (assume you've probably already done that). It's about not being able to get married or become common law - but it's also about having formed a relationship that is 'marriage like' from a financial, etc. perspective. So that's what you would want to prep for and can probably expect from the interviewer.
Good luck.
