It is pretty straightforward one refer to
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/medical-police/police-certificates/how/united-states.html
After filling out the FBI online form you have to submit physical fingerprints to the location they would ask you to send it. I would suggest finding a company near you in BC that does fingerprinting. Most Canadian firms seem to know how to do that, on an FBI form FD-1164. Folks in some threads in this forum sometimes advise you to do the fingerprinting yourself with stationary ink. Some have succeeded but it fails often and the FBI might reject and ask again etc which delays the PCC hence I would suggest avoiding that now that you have ITA. Please use reputed firms that follow a computerized version should cost 50-60$ or so per person. once the company prints your fingerprint form and courier it to the FBI to the USA address, you usually get this very fast. 3-4 weeks.
Otherwise, there are FBI-approved channelers in Canada, they charge you a Fortune usually 500$ or so per person and tend to be quicker and more foolproof. Most don't do it.
You should have done this when your partner created the EE profile itself, I hope you can get it before the deadline.