His attempt to escape deportation from Germany by hiding on a westbound freighter — under the cargo cover of a new BMW — was desperate and ill conceived. With only 1.5 liters of water and some nuts and dates, Walid Kabil did not have enough supplies, heat or space to survive the April voyage.

He feared being returned to Morocco, where he said he had been arrested because of his political activism. But cold, aching and dehydrated, he sought help from the ship’s crew.

Then came the surprise. After the ship docked in Halifax, Nova Scotia, and he was handed over to Canadian border authorities to make his asylum claim, Mr. Kabil was sent to a provincial jail filled with people accused of violent crimes, including murder.

Prime Minister Justin Trudeau has told asylum seekers on social media that his country welcomes “those fleeing persecution, terror & war,” but Mr. Kabil and thousands of others seeking asylum have found that the welcome does not always apply to them.

Government officials say only a small percentage of asylum seekers are detained because they could be a risk to public safety or disappear into the country. One expert on immigration said it was an important tool to control undocumented migration.

Like the United States and other Western countries, Canada is increasingly struggling to accommodate asylum seekers who some critics say are adding to a strain on government services.