Is it illegal to record others in their vehicles? My husband has been having an affair and she recorded us, would the both get subpoenaed to prove this?

I’m sorry to hear of what you are going through.  The recording device that your husband’s affair partner installed, and the secretly-recorded call, all come within the provisions of the Criminal Code which covers this kind of criminal offences. For example, for the secretly-recorded call, section 184 of the Criminal Code makes it an offence  to “knowingly intercept” (which includes “record”) a private audio communication by means of any mechanical or acoustic device, unless one of the people in that private conversation gives consent.  Since neither you nor your husband knew you were being recorded, the situation is likely covered by this section.

In terms of what to do, the short answer is simply this:  Go to the police; they will give you all the details around how to gather or preserve evidence that will establish the offence has been committed.