Hi Kelly,
Skip has nailed it basically

I also like to come through the Crowsnest Pass (Hwy 3) via Fernie and then from South take the Cowboy Trail up towards Black Diamond (now renamed to Diamond Valley covering Turner Valley & Longview), coming in via Okotoks and checking out the Sheep River around there (Campsite right on that River in Okotoks = Lions). You'll be entering Calgary from the South side.
If you come through the Crowsnest pass you will hit Sparwood (huge monster truck to check out for a few minutes leg exercise there!), as well Frank Slide (mining town buried) and then a huge rock in the middle of nowhere just west of Okotoks.
Fort Steele BC, Heritage Village is most certainly worth a stop at for a good couple hours or so if you've not done before.
Cute Town on the river as well with Hanging baskets on Steroids in the summer is: Fernie worth walking around, and there's some nice hikes/water fall nearby there.
There's also some goats grazing on the top of roofs in one of the small towns you'll pass by. As well some artsy crafty type crafts shops on your route.
We personally don't care for the Coquihalla Pass Northwards (huge drop offs and tight to them), but if you do end up coming through on the Trans Canada to North Calgary from BC, check out Rogers Pass summit and Golden and Revelstoke on your travels through. Likewise you'll be coming through Yoho National Park, Banff Nat'l Park and Canmore (nice town to explore along the river and the railroad trestles etc). The latter you'll hit coming through Radium and Invermere on the Hwy 93 Kootney's as well.
Hope some of that gives you some ideas to check into as to what might appeal best for you. As Skip stated you can't avoid mountainous terrain whichever route you take and over quarter century taking both routes into Calgary we've had no problems with initially a 36ft Fifth Wheel & Ford F350 as well our 36ft Gas Southwind Motorhome.
Enjoy beautiful scenery whichever you chose.
Safe and Happy Travels Kelly.