Yes, this is a perfectly correct sentence :)

It’s fine as “the greatest memory is the time” or “greatest memory is of the time” The second might be a tad bit better, as strictly “memory” isn’t a time but what happened at that time.

My greatest memory is OF the time I spent in Canada I think your sentence is OK , but as we have memories OF PERIODS OF TIME and living in Canada would constitute a period of time, then I would probably say it including the word OF . If there was a specific event like when you won the women's badminton cup at school, then yes you could say it without the OF. Eg My greatest memory is the time I won the badminton cup at school. But even there you might substitute the word memory for achievement. so My greatest achievement is the time I won the school cup for Badminton. Hope that helps Kind regards R