A rifle in VG to EX condition is, in my mind not supposed to have rust.
That been said, Canadaammo is a reputable business, I'm sure they will make it right, they have an excellent Customer service.
OP, I hope you called them before posting here.
If I was you, I would return the rifle and ask for a refund.
They I would buy one here on the EE from a reputable seller.
That way you will have the chance to see the condition of the rifle before buying.
Look for one with a blued finish, not the BBQ painted ones...