The Crowsnest Highway (Hwy #3) is a pretty old highway (opened in the 30's) and has not received a whole lot of upgrades over the years.
The drive from Osoyoos to Princeton is a non issue. Rolling hills of mostly 2 lane scenic road travelling much of the way beside a river.
Take your time (ie. don't push it) on the next section between Princeton and the East Entrance of Manning park. There are a number of reasonably tight downward sloping hairpin turns. Nothing that a vehicle of any size can't negotiate, you just need to be traveling at the correct speed (i.e.. slow down early before the corners)
From the East Entrance onward the drive through the park (including the pass) is very scenic and mostly easy going.
The only other part of the drive to be smart about is the downhill section a little past Sunshine Valley down into Hope, B.C. Lot's of opportunity to overheat your brakes if you push it too hard.
As mentioned above it's a fairly heavily travelled highway that you will see vehicles of all sizes travelling along.
2011 Jayco Greyhawk 31 DS