You need to keep good records of your expenses and revenues. You need to have a GST number when your income gets over a certain amount. You may operate as a sole proprietor or a limited company. Find out the benefits of each. Good sources of information are Canadian Business Service Centers , which are operated by the federal and provincial governments.
Every province has a toll free number.
You can also contact the Business Development Bank of Canada . There are also good books on starting a business as well as lectures and courses at local colleges or community centres. And establishing a relationship with an accountant is smart. You may only consult with this professional at tax time, but it is good to make sure when you are starting that you're doing every thing right.