Apex domains cannot have CNAME records.
Question and response
Question
dig s3-r-w.ca-central-1.amazonaws.com. NS
Answer
s3-r-w.ca-central-1.amazonaws.com. 5 NS ns-1386.awsdns-45.org.
s3-r-w.ca-central-1.amazonaws.com. 5 NS ns-1808.awsdns-34.co.uk.
s3-r-w.ca-central-1.amazonaws.com. 5 NS ns-270.awsdns-33.com.
s3-r-w.ca-central-1.amazonaws.com. 5 NS ns-737.awsdns-28.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0