Apex domains cannot have CNAME records.
Question and response
Question
dig tucows.com. NS
Answer
tucows.com. 5 NS ns3.tucows.com.
tucows.com. 5 NS ns1.tucows.com.
tucows.com. 5 NS ns2.tucows.com.
Authority
The response has no authority records.
Additional
ns1.tucows.com. 5 A 216.40.47.233
ns2.tucows.com. 5 A 64.98.148.121
ns3.tucows.com. 5 A 216.40.47.234
ns1.tucows.com. 5 AAAA 2604:4000:0:d:216:40:47:233
ns2.tucows.com. 5 AAAA 2604:4000:2000:2000:64:98:148:121
ns3.tucows.com. 5 AAAA 2604:4000:0:d:216:40:47:234
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0