Isn't the Okanagan on fire right now? Highway 97 is closed in both directions just south of Kelowna and the detour onto Highway 33 to get to Penticton from the south is going to add hours to your trip.
http://www.drivebc.ca/details.jsp?eventId=82758
And here's an inaccurate map of the fires:
http://www.kelowna.com/2009/07/19/unofficial-fire-map/
Anyways, have fun!
edit: I guess that by asking now on CP for suggestions you're not leaving for several days and have time for the fires to die down. Ignore my doom-and-gloom post then.