As a legislator who also heads the National Assembly, Guaido has immunity from criminal investigation that can be removed only by the Supreme Court.
Ruling left-wing SYRIZA party issued its own statement last week in which it expressed support for "the legitimate President" Maduro.
Freeland praised the role of Canadian diplomats in Caracas, who helped get the country's opposition parties to coalesce behind 35-year-old Guaido.
Food, fuel and medicine are in extremely short supply.
National Security Adviser John Bolton said President Nicolás Maduro and his allies could "no longer loot the assets of the Venezuelan people".
The Kremlin has also warned against negative repercussions should third countries intervene in Venezuela's affairs. Its proceeds must instead be held in blocked US accounts. Venezuela was the refiner's third-largest provider after the US and Mexico.
If a shortage of heavy crude develops in the U.S.as expected, it will likely increase prices throughout the North American market, including in Canada, said Kevin Birn, vice-president of North American crude oil markets for IHS Markit.
Venezuela's opposition leader Juan Guaido speaks during a news conference in Caracas, Venezuela, January 25, 2019.
"We denounce the illegitimate former Venezuelan Attorney General's threats against President Juan Guaido", Bolton said via Twitter.
The administration is using "a scalpel, rather than a meat ax", he said in an email.
Details of the sanctions are scheduled to be released shortly.
"The Maduro crime family has used PDVSA to buy and keep the support of many military leaders", Rubio said.
U.S. Secretary of State Mike Pompeo told members of the U.N. Security Council Saturday to "pick a side" in Venezuela.
But Senator Bob Menendez of New Jersey, the senior Democrat on the Foreign Relations Committee, said the Trump administration should brief Congress on its moves against Maduro.
Foreign Minister Sergei Lavrov also vowed that Russian Federation and its allies would "do everything" needed to protect Mr Maduro, although he didn't elaborate on what that would entail.
The sanctions threatened to hasten PDVSA's unraveling.
In Geneva, senior USA and Venezuelan diplomats traded jibes at a disarmament conference.
Last week, the Bank of England denied Mr Maduro's request to withdraw $1.2 billion worth of gold.