Question: Are US citizens still allowed to travel to Canada for work or other reasons?

A: Yes, but they should be prepared to self-isolate for 14 days on entry like all other entrants to Canada.

EDITED March 18/2020: Canada and US agree to close their shared border to non-essential travel

As of 4:30pm on March 16th, the Canadian border closure will take effect March 18 for anyone who is not a Canadian citizen, a U.S. citizen, or a Canadian permanent resident, with some exceptions including diplomats and airline crews. 

Airlines will be required to screen all passengers for signs of the virus and deny boarding to anyone showing symptoms. 

Overseas flights will be funnelled to just four airports in Toronto, Montreal, Vancouver and Calgary to allow the Canada Border Services Agency to better screen arrivals and ensure they are getting information that they are to self-isolate for 14 days.

According to Deputy Prime Minister Chrystia Freeland, Canada has asked people to limit non-essential travel, and all incoming travellers from the U.S. are being asked to self-isolate for 14 days. Dr. Theresa Tam, Canada’s chief public health official, said this should be a deterrent to anyone considering non-essential travel.

“Self-isolation for 14 days in Canada. That, I don’t consider to be something that a tourist would like to do for a holiday,” Freeland said.

Source: Canoe.com

See more on Canada’s travel advisories here.