Two ways, either through Merritt, lovely four lane divided highway, long uphill sections, or through Princeton, some two lane sections, a bit more scenic (IMHO). Both have stops along the way if needed. Almost the same amount of time. In July, the easiest would be through Merritt.
However, if your rig is heavily loaded and it's really hot outside, take the route through Princeton. The only way to keep your engine cool is to open the windows, shut off the air conditioning, and if you are really close to boiling over, pull over and give it a rest idling with the cab heater blowing as much hot air as you can to get the heat out of the engine. Tow trucks make a fortune on that road.
