Yes, they should be able to, as long as they are minors (under 18).
You have two options:
-apply for your citizenship and for them at the same time (family app).
-you apply for, receive your citizenship, and then apply afterwards for grant of citizenship for the two children based on having a citizen-parent.
I think the only difference between these is preference and whether you have documents ready, etc., and if there is any chance the 'joint' application for citizenship would be slower (I've no idea about that).
I can say the process in the second case is relatively simple and should not be too long (once you receive your citizenship). Since for children there's hardly any case for urgency, again, comes down for preference. (Obviously one thing is whether having Taiwanese passport vs Canadian would be a serious travel constraint/force you to get visas and fill out more forms etc.)
In most simple terms: if adoption is not yet complete, and you're ready to apply for citizenship, I'd just do that, and apply for it for the children later.
But again - mostly a question of personal preference. Obviously might be nice to have them become citizens and even participate in ceremony with you, but no legal consequences of that.