If you leave a good enough buffer between your LAS-LAX and LAX-YVR-YEG I think you'll be OK. There are at least 10-11 cheap WN flights any given day that you can catch for your LAS-LAX leg. Just catch the earliest possible one and you will be safe as they have flights every 1-2 hours and there is really no weather related delays to worry about. Don't bother with *A for such a short hop, WN is your best bet on this route as it gives you the safety of a lot of flights during the day, in case you need to be re-booked etc.