You are correct that freezing accounts and assets is far from unprecedented. It has been used (and abused) as a tool against suspected drug dealers, money launderers, ISIS supporters, and so on.
The difference here is its blank check authority against a reasonable protest objective as a response to certain bad actors within that broader objective and movement. Not everyone involved is creating criminal levels of noise pollution, trying to burn down apartment buildings, or blocking trade routes. Many of them just want good faith protest. If we could just arrest the bad faith actors quickly, and allow the good faith actors to continue protesting, we can simultaneously protect the right to valid protest while protecting the community within which the protest is happening. When you start freezing accounts without due process, that all flies out the window. This is what is importantly different about this particular action by Canada. It is uniquely chilling to the right to political protest in a way that unduly seizing the assets of suspected drug dealers isn't (although I am very much against that too).
The BLM protest movement can be used as an analogy. Would it be reasonable for all BLM support to be effectively criminalized by carte blanche freezing of accounts of people "involved"? No, of course not. The reasonable thing is to arrest those people who are looting or setting up CHOP or whatever, and to allow the real protestors to keep protesting.