Taking nothing away from the other (excellent) suggestions, I'm surprised nobody has proposed a one-way road trip that could include some time in the Canadian Rockies. Personally, I'd start in Salt Lake City, go north to Grand Teton NP, then into Yellowstone (adjacent) then up to Glacier NP. From there it's reasonably easy to run up to Banff and Jasper NPs in Canada. YYC is around 90 min. from Banff. IMO the Canadian Rockies should be on everyone's bucket list; others may disagree.

That would cut out at least one flight, which would probably cover the surcharge/difference in cost you'd experience with a one-way car rental between SLC and YYC. (Taking rental cars over the border is no big deal - done all the time.)