You may think that you will be able to buy marijuana legally as of July 1. You should think again.

Conservative senators are threatening to hold up passage of the two bills that would legalize cannabis consumption and toughen rules against abuse. Unless these senators yield, the bills are unlikely to become law in time for the Canada Day deadline.

"I think we have to do our job properly, and that means months," Conservative Senator Claude Carignan, the lead opposition critic on the legislation, said when asked in an interview how long he thought it would take the Senate to pass the bills.

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How many months?

"The House took eight months to study" the bills, he said. "It will probably take the same timeline to do our job properly." Given the summer recess, that would push Senate ratification to the end of 2018, at least.

The costs of missing that deadline would be severe. Provincial governments are negotiating contracts with suppliers, who are ramping up production. Governments and private companies are signing leases for storefronts. Police forces are acquiring new equipment, and training officers to identify pot-impaired drivers.

But businesses "take a risk if they adopt a plan … without legislation in place adopted by both houses," Mr. Carignan said. "My recommendation is to take their time and don't take an unusual business risk."

The political question is who will suffer more if the July 1 deadline is missed: The Liberals, for trying to force through legislation legalizing recreational marijuana use, or the Conservatives, for blocking the legislation in the Senate.

Either way, the Red Chamber's reputation – which had shown signs of rehabilitation since the expenses scandal – could be sent back into the depths.

"This is the old system going on," said a frustrated Senator Frances Lankin, an independent who was appointed by Mr. Trudeau. "This is the opposition trying to throw a spanner into the works of the government."

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Senators will start debate on Bill C-45, which sets out the terms for legalizing cannabis use and sale, and C-46, which sets out new laws for impaired driving due to marijuana use, when Parliament returns at the end of January. But Mr. Carignan believes the bills do not adequately address issues such as drug tests for workers, equipment and training for police forces, the impact of legalization on young people, and the tax implications for provinces. All will require careful Conservative study.

In the past, the government of the day would seek to appoint enough senators from its own party to gain control of the Senate and force legislation through. But Mr. Trudeau expelled the Liberal senators from caucus and has appointed only non-aligned independents. This allows the Conservatives to control the pace of debate.

The Senate could adopt the same approach used to pass the assisted-dying legislation in 2016: predetermined hours for debate; minsters testifying before the full Senate; and established timelines for votes that allow the bills to be sent back to the House for reconsideration if needed.

Passage "can easily be done by July 1," said independent Senator Tony Dean, who sponsored C-45. But the Conservatives see no reason to apply the assisted-dying approach to legalizing marijuana.

If the independent senators wanted to respect the July 1 deadline, they could form an ad-hoc coalition of the willing that could set and enforce deadlines for debating and voting on the two bills. But could such a herd of cats be willingly corralled?

André Pratte, another independent appointed by Mr. Trudeau, is not willing to predict. But if "there are people who are delaying the vote by tactics that only aim to delay, then I would be part of a group that would try to get us to a vote."

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The Senate will bear close scrutiny in the coming months, to see whether the Conservatives are truly willing to prevent marijuana use from becoming legal on July1, and whether the independents can organize themselves to push the bills through.

In the meantime, Mr. Trudeau might think about filling the 11 current Senate vacancies sooner rather than later. On C-45 and C-46, the coalition of the willing might need all the help it can get.