Canvas currently does not support restricted TA access such as only homework or quizzes. They give full access to assignment group for anyone who has a TA role in your course. Due to confidentially rule, I do not want my undergraduate TAs to access all the assignment details including midterm exams, final exams and course grades. I'm fine with graduate TAs have full access. I think canvas admin/programmers should understand the importance of this important option and make this available for the academic community soon.
As a comparison, Sakai LMS has this feature and instructor can decide what access you give to your TAs. I hope canvas will do the same soon to make canvas more helpful and useful.
One other issue canvas has is the weighted assignment option. Canvas currently does not have a way to weigh say all the homework equally unless they have equal point value. As you can see this is not practical in many situations. For example, we need to give more problem for one homework while another has few and at the same time want to weigh them equally. Again, Sakai has this option. irrespective of the point value, you can weigh assignments within one category equally in sakai. I hope canvas make this option available soon. Thank you.