Whats the best scenic train trip from Calgary to Vancouver?

there are really only two options: one is a year round service and the other, Rockie Mountaineer, is a private & very popular train tour that is becoming real competition for ViaRail (a distant Federal/ Crown Corporation)

Since I don't know where you are posting your question from or how familiar you are with Canada, I should mention that rail travel is very very basic in Canada. It is NOTHING like traveling on rail systems in France, Switzerland or other parts of Europe.

Rail service in Canada is limited primarily to the countries size. There are some short sections of heavily used rail travel in the Eastern (Ontario) parts of the country. But being that you're looking at some of the most remote parts of British Columbia, the train travel is limited. That is- noone takes the train if they have to be anywhere on time nor do many Canadians take the train over great distances: its simply much cheaper to get on an airplane. But if you have lots of time and enjoy scenery, the train could be for you.

One of the reasons the train stops in Kamloops (or.. the 'loops as I call it.. ) is that Rocky Mountaineer has the companies base in that small, central city.

That is: there are not alot of options of things to see or do if you make a stop there. Click on the "tourism Kamloops" link below. If you look closely at the photo's of the region, you can see it is Arid and somewhat dry in the summer time & cool and grey in the winter.

Kamloops is very much a large truck stop and has a fair bit of industrial areas with truck traffic for logging and transportation. It is- however- on the doorstep to some very remote parts of BC; the Blue River, Valemont and Robson Provincial park area.To rent a car and drive to these areas would be a full day trip just to get there. Hotels are somewhat limited on this lonely stretch of highway. Bus service is almost non existant.

The Via rail link below shows an excellent map and trip plan of a tour you may be interested in.

The Rocky Mountain Rail link is below as well.

You've picked a good one, though in truth there aren't really that many routes to choose from, and they all have great scenery especially if you're a first timer. You can hardly go wrong anywhere in BC for scenery. I kind of prefer the southern route, Crow's Nest Highway 3. A bit slower than Hwy 1, smaller towns and fewer of them, a little more rugged. The Columbia Valley south from Golden is a nice drive, and the Kootenays are very pretty with interesting history. Friend of mine stayed at Toad Rock Campground near Nelson last year and had a blast there. I like the Merritt area very much, but my favourite BC interior town is tiny Midway, right down near the US border on Hwy 3. If you're camping, it has a little municipal campground along the river and a very small bar almost across the street, at least it did last time I was through. Greenwood is a nice place to stop for coffee or ice cream.

Rocky Mountain Rail tours. It is expensive though. If you can afford the $$$ and time take your time and stay overnight in Golden.