Apex domains cannot have CNAME records.
Question and response
Question
dig ca-central-1.compute.amazonaws.com. NS
Answer
ca-central-1.compute.amazonaws.com. 5 NS ns-1991.awsdns-56.co.uk.
ca-central-1.compute.amazonaws.com. 5 NS ns-1129.awsdns-13.org.
ca-central-1.compute.amazonaws.com. 5 NS ns-491.awsdns-61.com.
ca-central-1.compute.amazonaws.com. 5 NS ns-924.awsdns-51.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0