Carrying Weapons North of the Border

I've been doing some reading in regards to carrying weapons north of the border. I had read previously that you can forget about handguns and assault weapons. I read today that weapons fall into three categories: allowed, restricted, and prohibited. Assault weapons and handguns fall into the prohibited category, but rifles with less than an 18.5 inch barrel fall into the category of restricted; which means that it is required to have an "Authorization to Transport" from each province that the rifle is carried. My factory manufactured Henry .45-70 has an 18.43 inch barrel! I have a small problem of understanding why these restrictions are on a factory manufactured weapon. My intent is for protection and possibility of participating in an Alaskan hunt.