Milk pouches have caught on in Canada
Not in this part of Canada they haven't. I don't have any data but casual observation suggests that on the shelves tetrapaks and plastic jugs carry about half the market each. With a very small percentage going to Avalon dairy who stick to traditional, and very heavy, glass bottles.
We bought milk in bags in Ontario because everyone did - and the price of the large multipacks made it economical to do so. I do not recall if we had blue boxes in Scarborough in the late eighties. And the pressure on the GTA's landfills was terrific.
Now the plastic jugs get recycled. I doubt the bags would. And anyway, aren't plastic bags a problem too?