Genuinely curious what those would be?
I think it's far from the most urgent issue our country is facing right now, but most of my objections to the monarchy would be moral or philosophical.
For one, in moral terms there is a lot of... let's say "historical baggage" that comes with the monarchy. For another, I don't think a hereditary system of governance is compatible with modern Canadian society (or at least what we would like to think it should be).
Not something that keeps me up at night, I don't think it will be removed any time soon mostly due to inertia, but I would definitely not be opposed to removing it.