As a Canadian resident and assuming that you are a Canadian resident you are taxable on your worldwide income. Your worldwide income includes any income you earn from being employed and being paid by your employer, to business income you earn from running a business, to passive income from your investment properties inside or outside Canada.
Canada's tax system is more or less based on an honor system where you'd report the entire amount of income you earn from all of your income sources. By not reporting your income you are putting yourself at risk of all sorts of gross negligence penalties that are pretty steep. CRA has its own ways and tools for tracking down any unreported income.
As an Uber driver you are considered to be running your own business and earning income from business. You must use the form T2125 (Statement of Business or Professional Activities) to report your income and expenses from Uber.
Yes. Any expense that is deemed to be reasonable in the course of earning income would be deductible. In your case, the portion of gas and maintenance expenses relating to your income would be deductible. However, you would not be able to deduct expenses relating to the personal portion of your auto use.