Apex domains cannot have CNAME records.
Question and response
Question
dig exchange.telus.com. NS
Answer
exchange.telus.com. 5 NS dns41.telus.com.
exchange.telus.com. 5 NS dns41.telus.ca.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0