I've never used Canvas before, but all the LMSes that I've used allow students to enable emails whenever anything is updated, including when grades are posted. This is off by default because it's often 10+ emails a day, because many teachers post notes once a day, and with 5 classes, that adds up pretty quick. I personally have it enabled because it's pretty manageable with some custom Outlook rules, but setting this up is well beyond the capabilities of most students.