The whole protest has been illegal from the start (violating the highway traffic act)
> Last week they arrested an old man for merely honking his horn to show support.
Source? Either way, yes, there was an injunction granted specifically against honking horns.
> So, anyone attending a protest is joining an illegal activity...and can have their accounts frozen.
No, anyone attending this specific protest at this specific time when there is a provincial state of an emergency (and now the invoking of the federal emergencies act, which requires provincial assent) is joining an illegal activity, and anyone providing monetary support to said illegal activity may have their accounts frozen.
> There's no guarantee of due process in Canada's constitution?
There is indeed. The Emergencies Act is subject to the charter of rights and freedoms, section 7 of which covers legal rights[1] and section 1 of which lays out how these rights are subject to "such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society". It'll be up to the courts to decide after the fact whether these restrictions were demonstrably justified (hint: with the province declaring the protest illegal, declaring a state of emergency last week, and the protesters totally refusing to move: they will be found justified. Our court system is not nearly as politicized as our southern neighbours')
[1] https://en.wikipedia.org/wiki/Canadian_Charter_of_Rights_and...