I teach 7th - 12th grade math in Canvas in an online school (we have some on-site components but class instruction is entirely online).
We use Florida Virtual for most of our core academic subjects. It's all online with no print textbooks. It includes both lessons (sets of webpages hosted by FLVS accessed as "External Tools" as far as Canvas is concerned - no additional student login is needed to view the lessons beyond being logged in to their Canvas class) and assignments (a mixture of Canvas quizzes and Canvas assignments).
I have spent a lot of time going through and editing the course shells they gave me to make them better suited to bothmy specific classes and Canvas in general than what I started with, and I would definitely say that it feels like a generic import designed to work with a wide variety of potential LMSes rather than something optimized to work as well as possible with Canvas specifically.
Example: each assignment is paired with a specific lesson, but the assignments by default do not contain any links back to those lessons or indications that there's something you should go find and do before completing the assignment. It's assumed that students are on the Modules page and interacting with their courses that way so they will see all course content. Our first year with Canvas, many students would click on the quizzes directly from their to-do list, take the quizzes, and then complain that they had never been taught how to do those things and why didn't their math class have anything other than math problems in it this year? I have now gone through an added a sentence like "Please complete Lesson: Dividing Rational Numbers before working on this assignment" as a description to all of the assignments and quizzes (sometimes with additional information/review options as I've noticed it being needed) so students are more likely to complete their lessons before doing the assignments, but "out of the box" none of that was in place.
I'd be happy to tel you more about my experiences with FLVS if you're interested - I've used their middle and high school math curricula for 3 years in two different LMSes now. I'm also interested in what other people are using for math curricula since there are both good and bad things about our current setup so I'm always looking to see what else is out there. (I suspect there is no perfect online math curriculum, since I never found a perfect print textbook either, but I'm going to keep looking...)