Again, you're confusing free trade with the maintenance of standards. If a country is dumping a product that doesn't meet our standards, we could react according to circumstances. If it's totally out of control, we could block imports of that product until that country raises its standards (notice, no tariffs, just outright blocked since it doesn't meet our standards) or we inspect at the border on a case by case basis.
Hong Kong, Singapore, and new Zealand have been doing this for a while now. If Canada needs help to implement it, we could just hire an expert from Hong Kong to advise us on how to implement it.
Now that I think about it, that's already the case in Canada. Only products that meet Canadian standards can presently legally enter Canada. The only question is whether they enter visa-free or not. Under unilateral global free trade, once it's determined that they meet our standards, we let them in visa-free. I assume we already have border guards keeping heroin out of the country, no?
That wouldn't change under unilateral global free trade. What would change is that once deemed to meet the same standard as domestic products are expected to meet, they can enter visa-free and we don't subsidize our own.