British Columbia's main highways are generally excellent for cycling, with ample shoulders. Where you have to watch out is on the downhill stretches through steep passes prone to gravel being washed onto the roadway. Sand and pebbles often accumulate on the shoulders and if you are coasting really fast, a pile might catch you by surprise. The Kicking Horse and the Rogers passes in particular are susceptible to landslides.
Also watch out for the Texas gates going in and out of Lake Louise, they are made of tubular metal. I made a mistake thinking I could ride over them in wet weather — I slipped and fell but was lucky I did not break a bone as my right leg went into the cavity.
Here are some photos of typical road conditions on Highway 93, the first is on the Icefields Parkway, the second is along the Kootenay Valley heading towards Radium Hot Springs.
This is Highway 16 heading up the Yellowhead Pass last summer with Mount Robson looming ahead. Despite looking so daunting, the climb around the side is not too steep, I did it on my middle chainring.