Am I subject to the CRA if I earn a living from the open source project I maintain?

No. If your revenue only covers your actual costs—including a reasonable salary or living expenses—then you are not considered to be monetising the project, and you would not be subject to the CRA on that basis. See What does 'actual costs' mean under the CRA? for more details on what counts as actual costs.

However, if you are making a profit (revenue exceeding your costs), this likely indicates you are monetising the project. See What does 'intention to monetise' mean under the CRA? for what constitutes monetisation under the CRA. In that case, you would be considered a manufacturer for the software you monetise, with corresponding obligations under Article 13.

Even in the monetisation scenario, your manufacturer obligations apply only to the monetised version. For example, if you offer both a paid "enterprise" version and a free "community" version, you would be a manufacturer only for the enterprise version. The community version would remain outside the CRA's scope provided you are an indivual and not an organization (see Can a solo maintainer be considered to be an open-source software steward ? for more on this distinction).