No. It is not possible to ensure that all your students receive email notifications about Announcements in Canvas.
Notification Settings: Students are able to customise their Notification settings in the same way that staff members can and can choose to turn off the notifications for Announcements. However, even if they turn this notification off, they will still see the Announcement when they login to Canvas.
Advice: If you are planning to use Announcements to communicate information about your course, advise your students to keep this notification turned on.