Crown Corporation means that the company is owned by the country - controlled by the government, not a private corporation.
A lot of the cost is due to economies of scale. There are 10X as many people using the US Postal Service, and a much smaller geographic area to cover. Because of this, they can do each piece for cheaper..
They also price *differently* than Canada. Here in Canada the 'First Class' or as we call it "Lettermail" rates are only for ... Letters. Depending on the bow, you can stick it into an envelope, but it needs to be less than 2cm thick... at which point it will ship cheap. Anything above the 'lettermail' size limits is a parcel -- and charged based on a combination of size and weight.
In the US, you can ship smaller 'packages' at the First Class (lettermail) rate, just paying based on weight - up to a limit. This means that a slightly bulky item like a bow can ship cheap because it doesn't weigh anything.
Online retailers have been fighting this battle for years, but it's unlikely to ever change... and to make matters worse, it's often cheaper to take the exact same package across the border, and ship it back across the border cheaper than shipping within the country.
Welcome to Canada, eh?
(If it's any consolation, larger packages cost about the same here as in the US)