Hi, i'm yet to start my first proper tour, but get around kelowna and the 30k around it regualrly on my comfy mountain bike.
Ive not cycled all the way to osoyoos, ive driven it plenty of times, and from memory i'd suggest the shoulder widths vary greatly, the area around peachland has some very narrow shoulders, there are however sections where its quite wide. In summary there's both good and bad. The highways tend to be driven very quickly so definitely consider bringing a rearview mirror.
33 seems the quieter highway for motorists but does get a large proportion of Big rigs and large trucks.
The road conditions are generally pretty good, but there is a big section on 97 (5k ish) where landslides have caused the road to be very narrow and full of gravel, also highway closures for a few hours each day have been in affect due to the clean-up so definitely check the bc highways website before setting out.
The kettle valley railway is very manageable when your on the trail proper, with firm trails with a light dusting of small gravel, the trestles have 10inch wide beams that are certainly rideable, but the number of people on foot usually means a short walk. The access roads to the trails are fairly ropey and more suited to MTB's with looser ground and lumps and bumps, but when on the trail the ground is very good and you could get away with good touring tires.
It really is a beautiful area with some stunning scenery, I hope your both wine lovers, as there is a winery every few miles it seems.
I'm sure you'll have a wonderful time