You can’t claim CCA against other income, only the income that you earned using the car (or other asset). Anything that you don’t claim this year will remain in your UCC balance, so you can use it next year if you need to.
In your case, you will have 2 separate UCC balances – one under rental income and one under self-employment. But if you feel that your self-employment (Uber) income will be large enough in the future, you may want to consider just entering the car in the self-employment CCA section, and only deduct vehicle expenses (fuel, etc…) on the rental income.
