I'm surprised Canadian coins are magnetic, though my two minute research says the loonie isn't? Apparently it was redesigned around 2000, maybe it switched then.
There is a sizeable community doing so called "magnet fishing". Check out r/magnetfishing
Coins don't seem to be their target, as very few seem to be magnetic.
Hm, true. But I sometimes see people walking along beaches doing this kind of thing. Though they're probably hoping for rings (gold, silver, diamond, ...) rather than coins, which would make it much more lucrative as well.
Gold, silver, and diamond are also non-magnetic.
Metal detectors, which is what they were describing, find metal that isn't magnetic.