The leaders of the powerful G7 industrial nations meet in Brussels Wednesday, intent on maintaining diplomatic and economic pressure on Russia, their former adversary-turned-partner-turned adversary once again.

It's the first time in 17 years that the group will meet without Russia. And it's the first time the European Union will play host, a role it assumed after the G7 leaders refused to meet in the originally planned venue, Russia's Sochi, to protest against Vladimir Putin's interventions in Ukraine.

"This summit will be an important occasion to take stock of the developments since the Ukraine elections two weeks ago,'' Marie-Anne Coninsx, the EU's ambassador to Canada told CBC News.

"It is very important that we stand together. That we are very firm in condemning what Russia has been doing."

Still, it is unclear heading into this week's summit just how effective economic sanctions on Putin's closest associates, and the companies they control, have been.

While Russia pulled back most of its estimated 40,000 troops from along its border with Ukraine, Putin shows no sign of relinquishing Crimea, annexed earlier this year.

And violence continues in Ukraine's east, where pro-Russian insurgents last week shot down a Ukraine military helicopter, killing all on board.

"I think the big picture is that those sanctions haven't had an enormous effect on the Russian economy or on the Russian body politic," says Roland Paris, director of International Policy Studies at the University of Ottawa.

"But I think the threat of additional sanctions, the solidarity that NATO, the West and the G7 have shown in the face of Russian actions in Ukraine probably led Vladimir Putin to calculate that it made more sense for him not to move those troops over the border into Eastern Ukraine.''

Stop meddling

Still, the withdrawal of troops is hardly a face-losing gesture by the Russian leader. And while officially shunned by his Western colleagues, he still dictates the agenda at the two-day summit, his actions and objectives still the main topic of their conversation.

For the G7 leaders, the message coming out of Brussels is expected to be that further Russian meddling in Ukraine will not be tolerated, and that the G7 will do everything it can to support Ukraine's new president, Petro Poroshenko.

He will be sworn into office on Saturday, the leader of a country that remains deeply divided, deeply in debt and deeply suspicious of its Russian neighbour.

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Ukrainian businessman and president-elect Petro Poroshenko will meet with U.S. President Barack Obama on Wednesday in Poland. (David Mdzinarishvili/Reuters)

U.S. officials, briefing reporters in advance of the G7 summit, insist that Russia needs to signal its willingness to work with Poroshenko to reduce tensions, something Putin has shown little inclination to do.

In this, Prime Minister Stephen Harper takes a harder line than most with Putin, referring to him in a speech last week as a leader who's growing "more comfortable with confrontation'' in Europe.

"His boldness has increased since Russian troops first made an open grab for power in Crimea,'' Harper said. "The impact of the Putin regime's expansionism and militarism extends beyond Ukraine. It threatens the security of our Eastern European allies and, by extension, the stability and security of the world."

Senior officials, speaking Monday on background, say Canada is willing to push for additional sanctions against Russia, including broadening the targets from individuals to specific sectors of the Russian economy.

"We cannot proceed as though the situation is normal,'' one Canadian official said.

Conflicting signals

Harper's tough line is popular at home with Canada's large Ukrainian-Canadian population. But it also plays well with other former Soviet-bloc countries such as Poland and the Baltic states, which turned to the EU and NATO.

Harper and U.S. President Barack Obama travel today to Warsaw to take part in the 25th anniversary of the landslide election victory of the Polish trade union/social movement Solidarity, an event that played a pivotal role in the collapse of the Soviet Union in 1991.

Harper will meet with Polish Prime Minister Donald Tusk to discuss the situation in Ukraine. Poland's ambassador to Canada, Marcin Bosacki, said Russia has created a very grave situation in Eastern Europe, especially in those countries such as Estonia and Latvia, which have significant Russian-speaking populations.

"We, the West, need to do three things,'' he told CBC News. "First, stop aggressive Russian behaviour.

"Second, help democratic Ukraine to more or less flourish as Poland flourished in the last 25 years.

"And third, ensure Eastern members of NATO are as secure as Western members of NATO.''

Still, some European countries are wary of ramping up the pressure.

RUSSIA

Happier times? Then U.S. president George W. Bush and Russia's Vladimir Putin shake hands before the G8 Summit session in St. Petersburg in July 2006. (Reuters)

Russia remains a key energy supplier to Europe, limiting just how far some of the G7's European members are prepared to go. The G7 leaders will discuss what can be done to keep oil and other energy supplies flowing, and to broaden the base of suppliers.

And then there's the conflicting messages some members of the G7 itself are sending to the Russian leader.

Putin, the jilted G7 host, remains an invited guest at the 70th anniversary celebrations of the Allies invasion of Normandy in the Second World War.

He is scheduled to dine with French President Francois Hollande at the Elysee Palace on Thursday, the evening of the anniversary, and he is to meet with British Prime Minister David Cameron following Friday's events.

Canadian officials say Harper has no plans to speak or meet with the Russian leader at the event, and neither does President Obama, his officials said.

A cold shoulder, apparently, for a leader who some believe is willing to revive the Cold War.