Good advice on the rapids, between Bromely Rock and Stemwinder there are several spots along the river that require (if you want to be confident about staying dry) significant experience in whitewater canoeing. Also note that the feel of the river will change a lot depending on water levels. I wouldn't recommend this stretch to somebody without good skills, experience and equipment (not meaning to imply that you don't have all that, I don't know), and I don't think it would be a good idea to have a motor hanging out one side, but i don't have any experience with motors on canoes.
If you're interested, here's a canoe club that offers some training for moving water, and there's some other courses too in the current newsletter, including on the Similkameen:
And here are a few photos of the Similkameen below Bromley: