Busloads of police arrived near Ottawa’s Parliament Hill, and workers put up extra fences around government buildings.
The biggest, most damaging of the blockades at the border took place at the Ambassador Bridge between Windsor, Ontario, and Detroit. Before authorities arrested dozens of protesters last weekend and lifted the siege, it disrupted the flow of auto parts between the two countries and forced the industry to curtail production.
“There is not really a playbook,” said David Carter, a professor at Michigan State University’s School of Criminal Justice and a former police officer.
The presence of children also complicated the planning.