Hi hottingert,
I find it easiest to just put my comments into Canvas, using speedgrader is the fastest easiest way. Students will see in the Canvas Gradebook a little icon to show they have a comment.
Through piloting Canvas, we have found it easiest to make sure that the grade matches PS each week, and let parents and students know PS is the official grade. However we have parents and students view all feedback and communication through Canvas. As the teacher I would make sure that the PS and Canvas Grades match, and if a student or parent finds any discrepancies they need to contact the teacher (which is usually because the teacher just didn't sync yet).