Sure. I'm happy to elaborate on that.
With the visitor visa, the legal test is whether the person will return home after they're finished visiting Canada. Anything about their situation, whether it's something to do with their attributes or with their behaviour, that might suggest they have no motivation to go back home after their visit is going to be a problem. You can imagine that when someone is married to a Canadian and wants to come to visit their spouse or common-law partner in Canada, one of the main suspicions in the mind of the officer is the motivation for them to go back home after their visit.
In the law, there is this concept called “dual intention”, which means that you can have a long-term intention to remain in Canada permanently but simultaneously have a short-term, legitimate intention to visit and go home while you're waiting for your paperwork to process.
I think this concept of dual intention is not very well used when it comes to spousal, common-law or conjugal relationships. It works very well for parents, for other types of relationships. However, there's something about the spousal relationship that makes officers disbelieve that the person is going to go back to their country, even when they have excellent ties to their home country, even when they have children they might be leaving behind in order to make that visit to Canada.
Something really needs to be done about that situation, because it creates so much pain for people.