Most of them don't have an opinion one way or another. Bernier, as you'd expect from a hardcore libertarian, is staunchly anti-interventionist. O'Leary has made noises in favour of peacekeeping,
though he managed to completely insult the military in the process of saying that. Erin O'Toole plays up his military background and is in favour of funding it more in the context of Canada's place in NATO. Scheer is vaguely in favour of fighting Daesh. Kellie Leitch is scared of non-white people, which presumably extends to how she feels about other countries. And that's about it.
In general, foreign policy is probably the most overlooked policy area in Canadian politics. Canadians will vaguely say that they care about Canada's place in the world, and you'll get the odd person who cares deeply about Israel & Palestine or China or Russia, but generally, it's not on the public's radar.
Here's a good rundown of it. It's part of a Russian smear campaign against her.
In NDP leadership campaign news, they now have their own accusations of racism. First Niki Ashton tweeted this a few days ago:
BLM Vancouver, naturally, couldn't let this stand:
So while the Conservative leadership candidates see who dogwhistle the loudest, the NDP is getting caught up in whether it's appropriate for a white woman to quote Beyonce.