Canadian consultants familiar with the country's negative experiences with CBI passports holders from St Kitts & Nevis, and the Commonwealth of Dominica, may be responsible for the new visa rule, and not any problems or issues involving Antigua. Dominica in particular has been a source of trouble for Canada, specifically Iranians holding Dominican CBI, and/or diplomatic, passports and citizenship*. A number of these individuals have been deported; others are presently being held, in custody, by Canadian immigration authorities.
Readers who wish further information, from an official source, may obtain it from Canada Immigration News. The Canada Immigration Newsletter, Canada Enforces Visa Requirement on Citizens of Antigua & Barbuda here.
* More details can be found elsewhere on this blog.