Need trip planning help! Western Canada to Vegas/Anaheim..

Time of year is up for debate. Would be great to be in NV/CA in winter, but I think the roads are too risky, possibly later in spring, but can still run into delays. We'll have the most flexibility time-wise in the summer when the kids are out of school (which is probably when we'll go..), but heat/crowds are less appealing.

Basically, we're open to suggestions there too!