In an interview with the Associated Press, Harper said Putin has the mindset of someone who believes the Cold War is still going on, and thinks that he can "change the ending somehow."
The prime minister said Russia had eroded any basis for belonging to the influential group of wealthy countries.
"I don't think Russia under Vladimir Putin belongs in the G7. Period," said Harper, who departs for Ukraine on Friday and will attend a G7 meeting in Germany on Sunday.
"Canada would very, very strongly oppose Putin ever sitting around that table again. It would require consensus to bring Russia back and that consensus will just not happen."
The G7 suspended Russia last year following the annexation of Crimea, which was part of Ukraine, but hasn't ruled out welcoming it back into the fold.
At an event in Toronto in which he announced stronger anti-terrorism measures on Thursday, Harper repeated his oft-expressed disdain for Putin's aggression in eastern Ukraine, where the war has killed more than 6,400 people since April 2014.
The world has to retain its strong condemnation of the actions of the Putin regime, he said.
"Whether it takes five months or 50 years, this country and the Western world — the free world — will never recognize the occupation of Crimea or any other Ukrainian soil by Russia — never," Harper said.
However, the prime minister ruled out sending any military hardware to Ukraine without the backing of Canada's allies.
Ottawa has sent 200 Canadian Forces personnel to Ukraine to train the country's forces. It has also offered financial assistance to help the country's struggling economy, including $202 million in development assistance and $400 million in low interest loans.
At the G20 summit in Australia last November, Harper gave Putin a less-than-warm welcome.
"I guess I'll shake your hand, but I have only one thing to say to you: You need to get out of Ukraine," Harper told him.
Harper said Putin denied being in Ukraine.
"This is kind of typical Russian foreign policy to just say black is white even though everyone knows the contrary," Harper told The Associated Press.
"As long as that's the view that they are going to take, that they're just going to treat us like we are all stupid, there really is no point in having a dialogue with them."
The prime minister's comments came amid word that renewed fighting in eastern Ukraine had shattered a truce deal and killed about two-dozen people, including five Ukrainian soldiers.
The conflict between Russia and Ukraine escalated last year when the Kremlin-backed president in Kyiv fled amid protests. Pro-Russian separatists took over the strategically important Crimean Peninsula, which Russia later annexed. The West doesn't recognize that move.
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