Hi, Little Hawk.

I believe the first question to ask is "Are they nature lovers or not?" If they are, they will like the parks, the rivers, birdwatching, etc. One special thing I remember is Ontario is the Oumet Canyon.

If they are not nature lovers, then museums, restaurants, picturesque neighborhoods, come to mind. And of course, Le Shopping.
I have a brother-in-law who says flatly, "I don't DO nature.")

The guidebooks always cover hot, loud music, whisky and gay bars, but I don't suppose that's what they are crossing the ocean for. That can be had anywhere.