It is very expensive! I trademarked a business name about 5 years ago because of the same concern. By the time all the info searches were done it cost close to $4000 to have a company do it for me. I was new, but there are probably ways to do it cheaper yourself. Keep in mind trademarking in Canada is only for Canada. You would also have to get a US and worldwide trademark as well. By the time you do all that you'd easily be in the 10k range to have it all done by a professional.
Save your money, and build your business first. Chances are you'll never have an issue. If you don't cover all your bases someone could legally take it anyway.
Trademarks and Trademark Registration In Canada