Eliminate cabotage. That offers airlines on both sides of the border much more flexibility.
For example now you could have Vancouver > Toronto > New York. Or NY > Vancouver > Seattle.
Those routes are illegal now.
If you think that by eliminating cabotage rules it would make for an easier/cheaper/more enjoyable travel experience, you're dreaming in colour. *Every* American airline would have you travel Toronto>NewYork/buffalo (or some other eastern US hub)>Seattle/LA>Vancouver