So you think it makes more sense to keep the terrorist here and use taxpayer dollars to "punish" him, and then once he has served his sentence, release him into the community to perhaps try and kill other innocent Canadians? Would you feel safe sending your kids to a school if such a person lived in your neighborhood? Would you feel good going to work in the morning if you worked in a building that had been targeted by such a person? I wouldn't.
As for the other country, it's not a choice that they have. Once a person is stripped of their Canadian citizenship, they have to go back to the country of their other citizenship, period. And, it's not a one way street either. if a dual Canadian-Australian citizen, for example, was convicted of terrorism in Australia, they would lose their citizenship and end up in Canada. And we would have no choice but to accept them. So why shouldn't we do the same?