Well it depends on what kind of roads you think are best. You could come through Kootenay National park to Radium, down through Cranbrook, Creston, Salmo, Castlegar, and then over to Grand Forks which has three mountain passes and good two lane road or;
You could get onto the tans Canada and go through Golden over the Rogers Pass to Revelstoke which is beautiful trip but busy this time of year. Then turn down highway 23 to Nakusp then #6 to 3A onto Castlegar and
# 3 over to Grand Forks which is a beautiful trip but...is very windy and narrow from Nakusp to highway 3A.
I've done both in my 40' but if I had my druthers IMHO I would stay on Highway 3 from Radium to Grand Forks.
1995 Monaco Dynasty 40'
1999 Suzuki Grand Vitara 4x4