Hi so i checked the new service from that portal,
- Provincial nominee program (non-Express Entry)
- Rural and northern immigration pilot
- Agri-food pilot
- Atlantic immigration program
- Start-up visa
- Self-employed people (federal and Quebec)
- Quebec-selected skilled workers, entrepreneurs and investors
- Sponsoring a spouse, partner, dependent child or other family
- Adopting a child through the immigration process
- Protected persons and convention refugees in Canada
- Humanitarian and compassionate grounds
- Temporary resident permit holders applying for permanent residence
- Home Support Worker Pilot
So it did'nt mention about the express entry program so i guess US citizen cannot apply for PR looking at the above list.
Since you said your husband is living in Canada, if he is a PR then definitely he can sponsor you through this "Sponsoring a spouse, partner, dependent child or other family" and yes he can create a an online account "
https://prson-srpel.apps.cic.gc.ca/en/login" and submit the application online instead of paper application.