Why is Saskatchewan an A and Manitoba a B?

When I was in The Pas recently I found there were significant concerns about the condition of Highway 283 which goes from The Pas to the Saskatchewan border and is the connection between The Pas in Manitoba and Nipawin in Saskatchewan.

On the Manitoba side of the border this highway is graded a B1 while on the Saskatchewan side it is graded an A1. Because it is not at an A1 level in Manitoba, there are limits on the highway's use for grain trucks and other commercial trucks. This is an important economic route and Manitoba's highway 283 should be at an A1 level. It is past time for the provincial government to make sure this happens.

By the way, I was told that large companies can get overweight permits for their trucks but independent farmers do not have that option. What is up with that? Why is the NDP government being "selective" when it comes to issuing such permits?