Technically, it's not illegal for Canadians to play on offshore platforms. But, and it's a big but, these casinos might not always be regulated or licensed in Canada.
Online gambling is legal through the Atlantic Lottery Corporation (ALC). Gamblers are allowed to gamble at offshore online casinos and sports betting services, as long as these casinos do not advertise their services in Canada or operate any of them from within the country. You must be at least 19 years old to gamble.