At this point in the US I really only see the plastic jugs for half-gallon and gallon sizes (~1.9 and 3.75 liters respectively), but the gallon size jugs are also used for water, especially distilled water like people would use in a clothes iron or CPAP machine. They also have half-gallon cartons, though, and any smaller sizes for milk have traditionally only been cartons, except sometimes if you buy milk at a convenience store like a gas station it will be in a plastic bottle like most of the other single-serving beverages.

I’m sure I’ve seen the gallon jug style in Quebec but don’t know what volume they contain, although from what I’ve seen with a lot of things when Canada went metric they just changed the labels but kept the same sizes.