Apex domains cannot have CNAME records.
Question and response
Question
dig custserv.ca. NS
Answer
custserv.ca. 5 NS ns-697.awsdns-23.net.
custserv.ca. 5 NS ns-1705.awsdns-21.co.uk.
custserv.ca. 5 NS ns-300.awsdns-37.com.
custserv.ca. 5 NS ns-1263.awsdns-29.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0