I, unfortunately, have to agree with blettiere. We were all ready to switch to the new PowerTeacher Pro Gradebook when we found out that the grade passback with Canvas was not working. In my district, I am lucky in that I only have a small number of people using this feature. At the last minute, we kept them on the old PS gradebook and moved everyone else to the new one (PowerTeacher Pro).
As far as the integration going the other way, it has been horrendous. We had numerous issues with bringing data over from PowerSchool to Canvas. Problems with enrollments being off and other issues with incorrect data went on for the past month, ever since we did our PS rollover for the new school year. In the past (for us, 2-3 years), it was as simple as calling Canvas and saying we are ready, and they'd remaster/sync/do their magic and all of our PowerSchool information would come over to Canvas and everything would be good. We asked them to sync every 4 hours, and never had a problem. Now we have been lucky if our syncs are every 24 hours and sometimes they just fail for reasons unknown.
I will say this: Canvas support has been, as always, outstanding. I have heard that PowerSchool is pushing selling their own LMS and are making it very difficult for other vendors to work with them. Like Brett, we are stuck with PowerSchool and deeply disappointed that something that worked so well has become so problematic. I am upset for Canvas, too, because it seems to me that PowerSchool is putting them in a very difficult position with their customers. But I don't know the inside scoop; I can only guess, like everyone else, at what is going on behind the scenes.
Our current status is that it looks like our data is coming over regularly and correctly now from PowerSchool. This is our first day back and no one is yelling...at least, not yet. As far as the grade passback, as long as you keep the teachers on the old PS gradebook, you should be okay. Once Canvas and PS get that fixed, we plan to move the rest of our teachers over to PowetTeacher Pro.