My understanding is that the legal link was created by the Emergencies Act. The government believes that it will be able to calm the situation faster if they can track and cut off the flow of money. This invocation gives the government increased powers to track (they ordered crowdfunding platforms/payment processors to register with FINTRAC). And increased powers to cut off funds (through freezing bank accounts).
Edit:
Here's a relevant quote from Canada's Deputy PM:
“The government is issuing an order with immediate effect under the Emergencies Act, authorizing Canadian financial institutions to temporarily cease providing financial services where the institution suspects that an account is being used to further the illegal blockades and occupations,” she said. “This order covers both personal and corporate accounts.”