Witmer resigned as the member of provincial parliament for Kitchener-Waterloo last Friday after McGuinty nominated her for the government job, freeing up her seat in the legislature.
The WSIB has a $14.2 billion unfunded liability, a staff of 4,000 and deals with 200,000 injured workers, and as a former labour minister Witmer is the right person to take on the challenges, said McGuinty.
"I think she’s worth every single penny that the public is about to pay her to manage this huge undertaking," he said.
"Witmer is one of those people who give politics a good name."
The New Democrats said previous WSIB chairs didn't even make the list of public sector employees earning over $100,000.
Former Liberal Steve Mahoney was paid about $130,000 last year as WSIB chair but was not on the sunshine list because he was part-time, billing on a per diem basis.
"The last WSIB chair didn’t make the sunshine list and was only a part-time employee," NDP critic Taras Natyshak told the legislature.
"The government is giving Witmer $188,000 a year as the WSIB chair, and it’s suddenly been made a full-time position."
Labour Minister Linda Jeffrey said the NDP were more interested in partisan shots than in improving things at the board.
"I think this sounds more like an election stunt than worrying about injured workers," Jeffrey fired back.
The opposition parties say the Liberals lured Witmer away with the plum post so they could force a byelection in her riding in hopes of winning the one seat they need for a majority government.
"The issue is not about how much Witmer gets paid," said Progressive Conservative Leader Tim Hudak.
"It’s about what the premier is willing to do to try to get out of a minority government situation."
At a campaign-style visit to Agfa Health Care in Waterloo, McGuinty acknowledged the voters of Kitchener-Waterloo will be deciding not just on a local member, but on the fate of the minority Liberal government.
"This is more than just choosing a representative for the riding," he said.
"It’s making a determination about a form of the government that we all look to here in Ontario, and that’s an important decision."
The premier also said it would not be fair to voters or the other parties if he called a quick byelection in hopes of catching the Tories and NDP unprepared.
"I don’t believe in snap byelections," said McGuinty.
"I believe in allowing all the parties who are interested to nominate a candidate. And I think it’s important to allow for a bit of time for people to adjust to the fact that the seat is now vacant."
NDP Leader Andrea Horwath agreed voters in Kitchener-Waterloo have an important choice to make, and urged them not to elect a Liberal and create a majority government.
"It’s an important byelection because it’s one that indicates to the rest of the people of this province whether they made the right choice in October. I would say they did," Horwath told reporters.
"I would say allowing a government that shuts people down, that doesn’t listen to them, that has a 'my way or the highway' approach in a majority situation, to get that majority back is not the right direction for us."
McGuinty has up to six months to call the byelection, and said he wants everyone to have "a fair and equal start."
The Liberals fell just one seat short of a majority in last fall's election, with 54 seats compared to a combined 53 for the Tories and New Democrats.