URI design, part 2

Thanks for your answers, it's pretty much what I had in mind.

I want to discuss a second example:

a)
POST /orders/1/cancel

vs.

b)
PATCH /orders/1

canceled=true


Does REST say anything in favor or against these two designs?

Personally, I would never do 'b' because it's simply hard to implement
with the tools I use. Also, isn't it a case of tunneling? 'Cancel' is
an action that does more than simply update a resource.

--
Max Toro