They're both excellent destinations. Where to go would depend on how long you have.

If you have lots of time then I'd recommend first crossing the border into Southern Alberta and do the whole Cowboy Trail and Badlands action, then work west into British Columbia, eventually finishing on Vancouver Island. You have lots of options to snake back towards home still going through some killer geography all through the US Pacific Northwest and western states.

One tip: Push the holiday as late as you can to avoid the insanely busy summer high tourist season. Also, if you can rig up to car camp (as well as using hotels/hostels/Airbnb/etc.) then you can check out some great campsites too.

Have fun with your research, that's a fabulous road trip.