Lawyers for the former and current MPs for Etobicoke Centre debated how serious clerical errors need to be before a new election is required, as part of a case at Canada's top court over missing paperwork from last year's federal vote.

Put another way, how easy should it be for Canadians to vote?

Conservative MP Ted Opitz is fighting a lower court decision that declared his 2011 election win null and void. The appeal to the Supreme Court of Canada is his only recourse to avoid having to fight another election against his former opponent, Liberal Borys Wrzesnewskyj.

Opitz's lawyer, Kent Thomson, argued Tuesday that Wrzesnewskyj hasn't proved irregularities in the May 2, 2011, election in Etobicoke Centre were anything more than clerical errors.

The question, Thomson argued, is whether polling station errors by Elections Canada staff can disenfranchise people from their constitutional right to cast a ballot.

Read a recap of our liveblog below

"It can't be trivial errors," Thomson said, arguing the case was a failure in record-keeping, with no evidence voter registration certificates weren't filled out, only that they are now missing.

But Gavin Tighe, the lawyer for Wrzesnewskyj, argued that it's important the paperwork exists so that Canadians know that the people who cast ballots were qualified to do so.

"It's the rules which give democracy integrity," Tighe said. "When we allow the system to fall apart.… We lose the rights for everyone else to vote in fairness.

"It's the right of the citizen to review what's gone on."

Loose rules could mean contested results

The Supreme Court is hearing Opitz's appeal of an Ontario Superior Court decision that overturned the 2011 federal election result in Etobicoke Centre following a legal challenge by Wrzesnewskyj.

Opitz won the riding by 26 votes, but Wrzesnewskyj successfully argued that clerical errors made by Elections Canada meant some of the ballots shouldn't have been counted.

At the heart of the case are dozens of missing or incomplete voter registration certificates, which allow people who are not on the voters list to cast a ballot once they have confirmed they are a Canadian citizen aged 18 years or older and live in the riding.

A lawyer for Elections Canada says the agency believes that if voters are qualified their votes should count.

"What's at stake is that if the rules are lessened to too great an extent then the result is going to be a large number of contested elections," Dave Di Paolo said after the sitting ended.

"Any time, in this hyperpartisan environment, we have a plurality that is too small, the inevitable result will be a contested election by the losing candidate."

Opitz said the Elections Canada staff were well-meaning people trying to do a job who made mistakes during a 14-hour workday.

"The issue is did anybody intentionally break [the rules]," he said. "Sometimes you forget — have you never forgotten to check off a box, or sign something? It happens. It happens."

On CBC News Network's Power & Politics, Opitz said mistakes might have been made by Elections Canada workers, but "fatal errors" were not committed in this case.

"I'm the MP because I was validated and verified by Elections Canada," he told host Evan Solomon. Opitz said if the Supreme Court does not rule in his favour he will have to step down right away.

Rules for proving identity necessary

Wrzesnewskyj's lawyer said there's a difference between being qualified to vote — being a citizen of Canada 18 years or older — and being entitled. Only those who live in the riding, or more specifically in the catchment area around a polling station, are entitled to cast a ballot at that station.

In some instances, an Elections Canada worker vouched for more than one voter in the riding. That's against the rules, Tighe said.

Voters can prove their identity and therefore their qualification to vote by:

Showing their voter identification card.

Showing two pieces of identification with their address.

Having someone who lives in the poll and knows them vouch for them.

"There has to be some rule with regard to proving who you are," Tighe said, arguing the system is designed to prevent harm from occurring.

Conservative Ted Opitz, left, won the May 2011 election in Etobicoke Centre by 26 votes, but Liberal Borys Wrzesnewskyj successfully challenged the result in court. The Supreme Court reserved judgment Tuesday in Opitz's appeal. (Sean Kilpatrick/Canadian Press)

The justices interjected frequently, probing both lawyers' arguments.

In his arguments, Thomson said Wrzesnewskyj's legal team had failed to prove its case since it didn't call any Elections Canada's workers to testify whether voters failed to prove they were qualified to vote or whether the workers had just lost that evidence.

Chief Justice Beverley McLachlin challenged him, wondering whether it's up to the Supreme Court to define how Wrzesnewskyj's lawyers proved their case in front of the Ontario Superior Court.

Thomson replied it is up to the Supreme Court to say whether Wrzesnewskyj proved his case.

Wrzesnewskyj said on Power & Politics that, beyond his own political future, there is a "grander issue" in this case.

"It's the integrity and the confidence people have in the integrity of the electoral system … it has been shaken," he told Solomon.

"Whatever the decision is, however it lands, I guarantee you that the next federal election in Canada will be run very differently and all of us win," he said. "If this process results with the Canadian public seeing that the system has been restored, our confidence is restored in our electoral process, it's a win."

Elections Canada wants new evidence considered

The hearing kicked off Tuesday with arguments over whether to consider new information provided by Elections Canada.

Di Paolo told the court Tuesday the agency didn't think the evidence was relevant during the Ontario Superior Court hearings into the case, but based on Justice Thomas Lederer's decision, it is now much more relevant.

One issue Lederer considered was whether those who cast ballots could prove they were Canadian citizens and therefore qualified to vote.

Since his decision to declare the 2011 result null and void in Etobicoke Centre, Elections Canada has found 44 of the voters on a national list of electors, which means they are citizens. Another lawyer for Opitz, Thomas Barlow, said that information would ease Lederer's concern over citizenship.

Tighe said the new information isn't relevant because Lederer had information in front of him that showed many voters were on the list and therefore Canadian, but they didn't sign a registration certificate used to confirm they were qualified voters, and therefore didn't fulfill the requirements for voting.

McLachlin adjourned the court at 12:30 p.m. ET, saying the would reserve judgment on Opitz's appeal and a cross-appeal by Wrzesnewskyj and on the motion by Elections Canada to submit new evidence.

Wrzesnewskyj is challenging Lederer's contention that voters can cast their ballots at any polling station in the riding as long as they are qualified.

The Supreme Court held the hearing outside of its normal schedule to speed up the appeal. This is the last arena for Opitz to argue to keep his job and for Wrzesnewskyj to make his case for a new election in the riding.

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