Yes, milk and processed dairy products (fluid milk, yogurt, cheese, etc) move in between provinces. We do this in order to meet the needs of Canadians and to ensure we are utilizing our dairy processing capacity to the fullest. This changes all the time depending on the season and the processor. For example, if a plant is shut down for repairs in BC, the milk may head over here to ensure there is no waste and fresh milk remains on your grocery store shelves.
Alberta, British Columbia, Saskatchewan, and Manitoba are part of the Western Milk Pool (WMP). Within the WMP, milk can move in between provinces, although it mainly stays here in the province. There are no trade barriers between moving milk or processed dairy products inter-provincially. The eastern Canadian pool is called the P5.
Don’t forget that no matter where this milk comes from, it needs to pass the same high quality standards anywhere in Canada. For example, the use of synthetic hormones in completely illegal in Canada and every load of milk is tested for antibiotics.