BRUSSELS—Belgian police were filtering traffic around the Brussels capital region during Monday’s morning rush hour in an attempt to keep a vehicle protest against coronavirus restrictions in check. Police narrowed some highways and imposed go-slow traffic to keep control of what it feared could otherwise turn into a choking demonstration like those by horn-honking truckers in Canada. Early indications didn’t show a groundswell of support for the action but police took extensive precautions in and around European Union headquarters in central Brussels. Many trucks were expected from France, where Paris police fired tear gas Saturday against a handful of demonstrators on the Champs-Elysees Avenue who defied a police order by taking part in a vehicle protest. A threatened blockade of Paris failed to materialize over the weekend, despite days of online organizing efforts. In the Netherlands, dozens of trucks and other vehicles—ranging from tractors to a car towing a camping …