In my letter of introduction (POE), it is said:
There is nothing stating that it will expire if I do not enter after 90 days or even if I change my program (or even institution).
Your application to study in Canada has been approved. A permit authorizing your studies will be issued to you
on your arrival to Canada following an examination by an officer of the Canada Border Services Agency, subject
to your compliance with the requirements of the Immigration and Refugee Protection Act and its Regulations.
The officer will ask to see this letter, your passport and may request to see your supporting documents, such as
the letter of acceptance from your educational institution.
...
You must seek entry to Canada to obtain your study permit by (2021/07/02). Your passport must
be valid beyond the period you intend to remain in Canada. If not, the validity of your study permit will not be
issued beyond the expiry date of your passport, or, for United States citizens and permanent residents, the
validity date of your identity document.
on your arrival to Canada following an examination by an officer of the Canada Border Services Agency, subject
to your compliance with the requirements of the Immigration and Refugee Protection Act and its Regulations.
The officer will ask to see this letter, your passport and may request to see your supporting documents, such as
the letter of acceptance from your educational institution.
...
You must seek entry to Canada to obtain your study permit by (2021/07/02). Your passport must
be valid beyond the period you intend to remain in Canada. If not, the validity of your study permit will not be
issued beyond the expiry date of your passport, or, for United States citizens and permanent residents, the
validity date of your identity document.
There is nothing stating that it will expire if I do not enter after 90 days or even if I change my program (or even institution).