Sure.
It is possible for Canada to go back to the court to seek an extension of time. In order to be successful, from past experience, we know that we cannot go too soon. The government has to show that it did what it had to do and did best efforts to meet the deadline. Granting a suspension of a declaration when legislation is declared invalid is a remedy. It's something that the court will not do lightly. Granting the extension it will not do lightly either.
Actually, the Supreme Court of Canada, in Carter in January this year, set a very high threshold, and indicated that it's only in extraordinary circumstances that such an extension will be granted.