ProfHacker’s section of the Chronicle of Higher Education has a few posts related to blog grading, such as
Also, Dr. Naomi Johnson and Dr. Heather Lettner-Rust have developed a blog rubric , which can be adapted across disciplines and student levels.
As for the process of grading, you may create a submit-by-url assignment in Canvas and grade each student post/e-Portfolio privately.
Student view of the assignment:
Instructor’s view of a student blog post in Canvas Speedgrader: