Is it going to be considered "essential" travel to let them go back home?

Or are they stranded here for the duration?

(My next door neighbor is an example)

It might soon be impossible to get on a flight.

The government has officially stated that any Canadian citizen or permanent resident or person directly related to those two classes who presents at the border will be allowed in. If they are symptomatic they will be given appropriate directions, and treatment if serious enough.

However, nobody has a right to board a flight, especially if they are symptomatic. So they might be stopped before they get near a border. The government has announced that nobody should expect mercy flights to Canada.

The government is offering financial assistance for people needing to come home including loans for transportation and expenses.

They are not required to come home. They may have appropriate health insurance for the US and other exigencies. Some have already decided and let it be known they will not be returning for the duration.

I'm not sure how this affects certain residency / visa requirements some people may face.

For now, Amtrak's long distance services are still running, for example from Miami to Niagara Falls NY via New York Penn Station. My wife & I took the train from Buffalo to Miami a few years ago in better times.

The problem might be trying to get a cab across the border. Not sure if that would count as "essential" travel. All that assuming the traveler is symptom free of course.

Ran into a lost Quebec couple trying to find some tour on the Rio Grande.

They were driving, and far from home. (Then again, it's not like I was especially locked down. Did get to see where part of the wall is planned for, the Las Lomitas chapel, that sort of thing.)

If that daily commute is shut down, jobs will be lost.

or over the Ambassador bridge (much of the truck traffic). Yup.

Same with the couple bridges going between the "Niagaras" - Canada/U.S. (e.g., Peace Bridge/Rainbow Bridge) and through Blaine in Washington State.

who cross the border each day for work. They will still be free to cross. I have a friend who owns a manufacturing plant in Buffalo. She will be free to cross. Trucks, planes and trains carrying cargo meant for businesses, food etc. as well as drivers, pilots and so on will be able to cross. Considering that trade between the 2 countries is over $2B PER DAY, the economy would grind to a halt, especially in the auto industry. And I understand that certain car-making facilities are looking at gearing up to produce ventilators and other materials necessary for healthcare.

Going to take a few days to sort this all out, of course.

As for snowbirds coming back home, as long as they carry Canadian passports or other documents that show they are permanent residents, they'll be fine.

Definitely can't halt the trade!.

Cutting off access to your largest trading partner when there is no food in the grocery store is a bad plan. Supply chains are already a mess.

Social distancing is a good idea but that is between people not Countries. It is not a foreign virus.