Have a look at AC, you would connect at Toronto and clear US customs there which, reportedly can be better than clearing at a US gateway. You don't have to enter Canada either. Hopefully their prices would be competitive as well.
Not exactly true. You would still have to clear Canadian immigration and customs upon landing in Toronto, then proceed to connections where you would clear US immigration and customs in Toronto. This means you will arrive in Las Vegas as a domestic passenger and so will be much quicker to get out the airport there.
However, it is an option to consider.