The US opened its borders to Canadians Monday after being mothballed for almost 20 months, but there are a few catches.

American border guards will ask Canadians if they have been fully vaccinated for COVID-19, and the personnel will do random checks requiring proof of inoculations.

- We are going to ask you if you are fully vaccinated - Jeffrey Toth, program manager with the CBP's (U.S. Customs and Border Protection) Buffalo, New York division told the Canadian Broadcasting Corporation. -You may be asked to provide proof.-

Those who do not have the proof of vaccination will not be allowed to enter the US. Canadians will need to be patient, as the CBP is expecting heavy traffic.

- For travelers making the trip to the United States, we ask for patience with our officers - said Matthew Davies, the executive director, admissibility and passenger programs, with CBP. "To help reduce wait times and long lines, we encourage travelers to have the correct documentation ready."

The border has been closed to non-essential travel since March 2020. Canada reopened the border Aug. 9, 2021 to fully vaccinated Americans but the US held back until now.

More than 3.6 million Canadians flock to Florida each year to escape the harsh winter weather. While the border closing slowed the exodus the past two years, some had their vehicles taken to Florida by car-carrier service while they flew to the southern state. The border closure only applied to land travel.

But coming back into Canada now comes with a price tag.

All those returning must show a recent negative molecular test, such as the Polymerase Chain Reaction test - it detects viruses such as COVID-19. The test can cost up to $300.

Travelers who plan to stay in the US for 72 hours or less can take the test in Canada.

According to the Los Angeles Times, the same protocol holds true for the reopening Monday of the US-Mexico border.