As mentioned in the post above, what constitutes as European is decided by the European Council and European Commission. You are correct in that it is a requirement but there is nothing stopping them from going "Canada is European, as it shares our values, ideals, and ideologies". The decision does not have to be geographical.
It's unlikely and kind of a "the rules don't say a dog can't play basketball" type move but it's technically valid.
The definition of what classifies as European is up to the assessment of the European Council and the European Commission and need not be defined by geography.
III. CONDITIONS OF ACCESSION a) The European State
The sole material condition laid down by Article O of the TEU is that the applicant must be a 'European State'. There is no unequivocal interpretation of that criterion. It can be read equally well in geographical, cultural or political terms.
In 1987 an application to become a Member of the Communities was received from Morocco. The application was rejected by the Council on the grounds that Morocco was not a European State ( 7). In the case of Turkey, Article 28 of the Association Agreement signed in 1963 incudes the option of Turkey's eventually acceding to the Communities. Turkey in fact lodged an application to accede on 14 April 1987. Historically, Turkey has formed part of the so-called 'European concert'. Although part of Turkey's territory is located geographically in Asia, Parliament, the Council and the Commission have confirmed Turkey's eligibility ( 8). This example shows that the term 'European State' need not be interpreted in a strictly geographical sense. It is at all events a criterion subject to political assessment.
https://www.europarl.europa.eu/enlargement/briefings/23a2_en.htm
In other words if we decide that Canada counts, then Canada counts.
https://www.europarl.europa.eu/enlargement/briefings/23a2_en.htm