A witness can be arrested pursuant to a warrant under the Criminal Code. There is a specific power to do that in certain limited cases, such as, for example, where a witness is about to abscond. Under section 707 of the Criminal Code, there's a scheme set out for how long a witness can be detained pursuant to that arrest warrant. The absolute maximum period is 90 days, but, as I said, at least every 30 days the judge has to review whether the witness should continue to be detained.
On November 19th, 2012. See this statement in context.