Apex domains cannot have CNAME records.
Question and response
Question
dig s3-w.ca-central-1.amazonaws.com. NS
Answer
s3-w.ca-central-1.amazonaws.com. 5 NS ns-1196.awsdns-21.org.
s3-w.ca-central-1.amazonaws.com. 5 NS ns-409.awsdns-51.com.
s3-w.ca-central-1.amazonaws.com. 5 NS ns-618.awsdns-13.net.
s3-w.ca-central-1.amazonaws.com. 5 NS ns-1636.awsdns-12.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0