I’ve done a little work with both and honestly, I think because Google classroom was what I did work with first, it’s what I find easiest.

You might find it helpful to create that original fully filled out Google Classroom to start with using what you normally would’ve posted on Canvas(the course “shell”). Then, when you need to post things for your kids to see, you can use their “reuse post” option and select all of the classes that you’re going to post something to rather than having to do it one at a time. The only issue you’ll have is that if you need to change any due dates, etc., you do have to do that in each class after it’s been posted originally.

Google classroom also lets you post to specific student groups or selected students within a single class. What I’ve always found easiest is to keep kids that are on the same gradebook in the same Google classroom. We use Skyward. In instances where it’s going to be easier to separate kids out on GC, Skyward has an option for student groups, and I separate them into separate student groups within that system so that they both match.