Many people give money to charitable organizations. If a charity is registered with the Canada Revenue Agency, it will have a Registration Number and can issue tax receipts. If you are wondering if a particular charity has charitable status, CRA's website has a searchable database on their website:
Unfortunately, there are people who will take advantage of your generosity. Never let someone pressure you into giving on the spot. If someone comes to your door and doesn't have ID visible, ask to see some and make note of the name of the person. Be wary of phone calls where strange numbers are displayed. This could be an indication of someone deliberately trying to hide their identity. Ask questions about the organization. Some organizations will use names similar to well known charities in an attempt to deceive you. If you have any qualms, don't donate until you can verify that you are dealing with a legitimate charity. Check the link above to verify the organization has charitable status.
Report any suspected fraud to the Canadian Anti-Fraud Centre at 1-888-495-8501 or via their website: