Experts warn that a post-Brexit United Kingdom will present Canadian business with tremendous uncertainty about billions of dollars worth of trade and investments, no matter how the British Parliament votes on Saturday.

The outcome of the unusual weekend vote in London is itself far from predictable, as British Prime Minister Boris Johnson struggles to get support for a controversial agreement that he reached Thursday with the European Union.

But observers say even a Johnson success would only provide a starting point for further rounds of difficult negotiations between London and Brussels and eventually between Canada and the United Kingdom.

Fasken partner Clifford Sosnow says the primary benefit of Johnson’s plan is that it would provide for 14 months to 36 months of negotiations on a new trade deal for two of Canada’s biggest export and investment markets.

“The major concern for everybody is the instability and the instability from not knowing what the business relationship will be, what the investment relationship will be,” says Sosnow, who provides strategic advice about international trade and investments at one of Canada’s largest business law firms.

He adds that open talks between the United Kingdom and Canada would be allowed only after the U.K. leaves the European Union on Oct. 31, if Johnson’s schedule is passed by the British House of Commons.

The United Kingdom by itself, represents one of Canada’s top five destinations for investments and top 10 markets for goods and services.

It has also been a gateway for Canadian companies that do business in the European Union, which is Canada’s second- or third-biggest trading partner after the United States and China, depending on the measure.

About 40% of Canadian trade in merchandise with the EU goes through United Kingdom, says Achim Hurrelmann, a political scientist and co-director of Carleton University’s Centre for European Studies in Ottawa.

Without a good free-trade deal between Brussels and London, companies may reconsider “whether they want to stay in the United Kingdom or . . . go to Dublin [Ireland], or to France or to Germany or the Netherlands.”

“To some extent, that has already happened but my impression is that most companies have been staying put and observing and waiting [to see] what is happening,” Hurrelmann says.

He says that Johnson’s proposed deal would provide more time to sort out the U.K.’s trade relationship with the EU but also with Canada.

“Canada wants to have a trade deal with the U.K. and the U.K. wants to have one with Canada as well,” Hurrelmann says.

“But the question, of course, is will we have time to actually work that out properly or will that have to be very rushed after a no-deal Brexit.”

Mark Camilleri, a Brussels-based Canadian at the Canada EU Trade and Investment Association, says he thinks it’s fair to say “that having any deal is better than having no deal” if only to reduce uncertainty.

He says that having no U.K.-EU. deal “it would potentially be very destabilizing for businesses, including Canadian businesses that are not just based in the U.K. but also based in the EU that are trading to the U.K.”

But Camilleri noted the British Parliament has rejected Theresa May’s proposals on three occasions so “one has to hold one’s breath as to whether or not [Johnson’s deal] will get through.“