True enough, Milnews.
However, there is a big difference. In the Arrar case, the Canadian governement, through the improper actions of the RCMP, was found to have been the cause of Arrar's deportation to another country to face unwarranted justice for acts he did not commit (At least, that is the final narative from the various Supreme Court cases).
In the case of "terror travelers" like the present instance, these people voluntarily exited their country of origin to enter another country and commit acts there that may attract "proceedings" against them locally. In such case, Canada, or any other country, not only has no obligation but has no power to interfere in the justice system of such foreign countries - save to provide consular assistance where possible. And consular assistance, BTW, does not include providing in any way for the legal defence of such Canadian, nor their repatriation - unless they are a country we have Treaty with to permit repatriation after the trial in order to serve their sentence pronounced by the foreign power but in a Canadian jail. We have very few such treaties and they are usually with other Western democracies.