Belize City is not a safe place. I would not recommend spending time in the city, but once you are in the island of Ambergris Caye, yes, you are safe. All of the islands of Belize are safe to the extent that you do not leave yourself wide open.
You don't leave your Nikon camera on your golf cart seat and walk away because it’s not going to be there in half an hour (and it wouldn’t be there in Canada, either). You should not leave your Samsung smart phone down on your towel, go for a swim, and expect it to be there. You might be able to do that in a resort compound with full staff and security, but most likely, there is a chance it might not be safe either because everybody passes through the beach. People need to be smart. They need to travel with sense above them, and if they do that, they will generally be fine.