The government needs to find new revenue sources to help fund public transit and infrastructure projects, and letting drivers buy their way onto HOV lanes could be a "voluntary" way to help raise money, said Sousa.
"Those lanes are available to those that wish to pay for them. They work in other jurisdictions, and it’s something for consideration," he told reporters.
"You don’t have to use them if you don’t want to, but should you want to and you’re single in the car, there’s an opportunity there to revenue source some of that initiative as well."
Premier Kathleen Wynne said Monday the Liberals were considering road tolls or some form of tax to fund public transit expansion in the Toronto-Hamilton area and to pay for upgrading municipal roads and bridges across Ontario.
Letting drivers who are alone in their cars pay a premium to ride in the HOV lanes is just one option under consideration, said Sousa.
"Our government has invested heavily in the last nine years in infrastructure and public transit, (but) we need to do more," he said.
"We need to make it sustainable and we’ve got to find ways that work."
The Progressive Conservatives said they would not impose tolls on existing roads, but weren't saying how they'd fund transit and infrastructure projects other than to say they squeeze all efficiencies out of the system.
"When it comes to putting tolls on existing highways ... that’s not on," said PC Leader Tim Hudak. "I think that’s punishing drivers because it’s something they’ve already paid for in taxes."
Looking for new revenue tolls or taxes should not be the government's first option, added Hudak.
"That should be a last resort, not a first instinct," he said.
"I want to be sure in our plan that before we go back to taxpayers for a dime more, that we make sure we squeeze every dollar we can by making sure we eliminate waste in our budget and signal we’re heading in the right direction by balancing the books."
The New Democrats have said they don't support new taxes or tolls to pay for expanding public transit and repairing roads and bridges, and want the Liberals to close corporate tax loopholes before trying to raise more money from people.
"People see their government asking them to get ready to dig deeper again," said NDP Leader Andrea Horwath.
"They’re paying more, and they see Ontario’s largest corporations getting more than $1 billion in new tax breaks _ new tax loopholes _ opening up for them."
Ontario has HOV lanes on Highways 403, 404, 417 and the Queen Elizabeth Way.
The government says drivers using HOV lanes in the Toronto area save between 14 to 17 minutes per trip compared to their travel time before the HOV lanes opened.
Currently in Ontario, a bus of any type can use an HOV lane, even without passengers, as can emergency vehicles.
Single-occupant taxis and airport limousines are permitted in HOV lanes until July 1, 2015, as are drivers of electric vehicles with green licence plates, even if there is only one individual in the car.