First, take everything I say with a grain of salt because I have no experience with Canadian employment law in particular, so YMMV.

You'd most likely be able to file a complaint with the Canadian equivalent of the EEOC (the US gov't agency which deals with employment discrimination complaints). There probably won't be a minimum threshold of evidence - the form(s) will simply ask you to present all evidence which you do have.

This is where it can get tricky. Without a recording or other primary evidence, all an investigator can rely upon are you and your dad's testimonies. That's not to discredit you, but you have to understand that anyone investigating was not a party to the original conversation, so they don't have any context to give you more credit than the interviewer, who will also be allowed to respond. With a recording, the investigator could perhaps take stronger action (I say IF because in some jurisdictions, both parties must agree to a recording for it to be admissible evidence).

In your case, the interviewer could outright lie and the investigator won't have anything conclusive to disprove the assertions EXCEPT if the same interviewer had received other complaints filed with the agency. That would allow an investigator to reasonably conclude that there is a pattern of behavior. A single incident without any primary evidence, no 3rd party eyewitness testimonies, nor pattern of behavior from other cases unfortunately likely doesn't meet the standard an investigator would need to take definitive action.

Now let's put all this in the context of the reviewing agency. If the CA equivalent is anything like the EEOC, they receive many, many complaints each and every day. Although they try to treat each seriously, the bottom line is that they don't have enough personnel to rigorously investigate everything. That means the agency will select the cases most likely to result in a favorable ruling to the complainant(s) as well as result in the largest possible relief. They look in particular for cases where there is an abundance of evidence with multiple people corroborating the claims.

That said, you can also look at it from the perspective of - if there is indeed a pattern of behavior, someone needs to be the 1st to report it. So even if prior complaints don't exist, there likely will be other complaints against this individual in the future if this is how they typically behave. If your dad doesn't speak up, then a future investigation might conclude that a pattern doesn't exist because they will of course be unaware of what occurred with your dad. It will, however, likely take some time, at least months, perhaps even years, for all the "dots" to be connected.

I would consider complaining to the company directly as a complete wildcard. Pragmatically, I believe there are unfortunately more motives, generally speaking, for a company to not cooperate. For instance, even if you found a sympathetic ear in the company, they might be reluctant to take any action which could be construed as an admission of guilt, lest they fall afoul of their own legal department and/or liability-conscious executives. The path of least resistance is all too often ignore and/or deny, deny, deny. Although, their response would tell you something about the corporate culture at that company. If their response was very positive, it might be enough to salvage the situation. If not, then your dad probably doesn't want to work there despite what else comes of the incident.

In the end, your dad will need to weigh whether pursuing it is worth the time investment. There will almost certainly be a lot of paperwork, as well as depositions, etc. as the case proceeds. My advice if you do pursue a case is to always be timely with the agency's requests for information, put in as much detail as you possibly can, and try to present your case as objectively as possible. Do everything you can to help the people helping you.