Ive been making the trip from the prairies to Vancouver Island all my life. I've pulled sailboats, driven truck campers and made at least 50 car trips.
The drive from Calgary to Vancouver on the transcanada hwy is spectacular and not to be missed. Calgary and the prairies are at 3,000+ ft elevation, the trip from Calgary to sea level is net downhill. You will burn less gas going west than east.
I suggest making the return trip via the northern US states, as the incline to the continental divide is more gradual. Idaho is worth the trip and Montana has many wonderful lakes and attractions.
HWY 3 via southern Alberta is also a good option. Keep in mind that this corridor is extremely windy. sports teams in southern Alberta are usually called the Hurricanes.
My favorite drive is the Canadian Rocky Mountains. An Rpod is the right trailer for this trip, allowing you to stop and take in the sights and the spectacle. If you want more detail, let me know. We're driving over the Rockies to Vanc Isle March 21. Will stop in Golden and the Shuswap.
If this is your one and only trip over the Rockies, I would also suggest a detour through Vernon and Kelowna, which will add about 45 minutes to over-all driving time. Kalamalka Lake will make your jaw drop.