That’s not really true. The US has 5% of the quota, tarrif free. Which they don’t even fully use. But, to be sure, it does get used. You absolutely can buy American milk products in Canada.
The problem is that they have to go through the processors to satisfy the processors' own quotas so by and large the meager 5% isn’t worth the operational complexity vs just buying milk locally for the processors. The US wants to be able to go directly to the grocery stores.
what changes is parts that arent so visible - milk powders, sugars, proteins, etc, that are inputs into ultraprocessed foods like a cheezit
I mean, what were you expecting? Like before, they only have access to 5% of the market tarrif-free, and, in practice, cannot even use all of that due to the practicalities of 5% not being all that operationally useful to the Canadian processors. The US hasn't been bemoaning these tariffs for longer than I've been alive (and I'm quite old by HN standards) because the market is flush with their goods...
> It's extremely hard to find non-Canadian liquid milk on Canadian store shelves.
Hard is a long way from never. Yes, the volume is negligible, but known to be non-zero. Although we'd really have to understand the makeup of the milk to know how common you consuming it is. If every jug has a tiny drop of US milk in it then the chances of you encountering US milk on store shelves is actually quite high. It is highly unlikely that any jug will be 100% US milk. It is not like anyone is going to take the time to painstakingly separate it into a separate tank before bottling. Milk is milk.