Of course your son can drink fresh milk if he want to. I live in Canada and our kids will start to change to drink fresh milk (whole fat) after they reach 1 year old. However, I know kids in HK are still used to drink formula until they are 3 or 4 years old.
My daughter is now 19 months (26lbs) and she like to drink fresh milk lot more then formula since she turned 1 year old.
Yes, milk in Canada is cheap, we only pay about CAD4 (around 25 HKD) for 4L milk.
Actually, we are now in HK for holiday and we've tried many different brands like those from HK, Japan and Austraila and 蒙牛. I found that milk from Australia and 蒙牛 are very 奶味濃郁.
Also, I dont think it has any different between包裝 and冷凍柜位的奶. Usually I will 座熱給BB喝 when we are at home (even in Canada). or will just give it to her when we are outside.
My BB liked 十x牌 before. However, after he tried 蒙牛, he doesn't like 十x牌 so much now.
For 蒙牛, I just poured into bottle and let him drink it. For 十x牌, I would 座熱"給BB喝 as it is too cold taking it from fridge.