Do you recommend using a standard business letter format for cover letters or using the same heading from the resume?

If you are applying to a job in finance, keep it conservative and standard. The trend is back to traditional values in finance given all that has transpired.

Your resume is a marketing document, and the header does not work well in a cover letter. But the contact information should be consistent.

If you want to be matchy matchy use the same core font in the cover letter as in the resume.

If you are sending the resume and cover letter today, I believe they should be branded. So, use the same header on all the documents you send together for branded consistency.