TORONTO — Tired but smiling, an 18-year-old Saudi runaway who said she feared death if deported back home arrived Saturday in Canada, which had offered her asylum in a case that attracted global attention after she mounted a social media campaign. “This is Rahaf Alqunun, a very brave new Canadian,” Foreign Minister Chrystia Freeland said arm-in-arm with the Saudi woman in Toronto’s airport. Rahaf Mohammed Alqunun smiled broadly as she exited an airport arrival door, capping a dramatic week that saw her flee her family while visiting Kuwait and before flying to Bangkok.