MONTREAL, June 30 (Reuters) - A strike by WestJet Airlines' mechanics that has led to hundreds of canceled flights over Canada's long holiday weekend will continue until a deal is reached, the union's president told Reuters on Sunday.

Bret Oestreich, president of the Aircraft Mechanics Fraternal Association, said the two sides will reconvene with a mediator on Sunday. The union represents around 680 workers at WestJet, including aircraft maintenance engineers, who went on strike on Friday after 97% of its members rejected a pay deal reached in May.

"All we want to do is to go back to the table," said Oestreich. "The strike will be in effect until we get an agreement."

He said the two sides are separated by a first-year economic difference of approximately 7%, or less than $8 million, on a roughly four-year contract.

WestJet Airlines said on Sunday that it had canceled an additional 410 flights overnight, for a total of more than 800 flights, as the strike entered its third day.

"WestJet is in receipt of a binding arbitration order and await urgent clarity from the government that a strike and arbitration cannot exist simultaneously," airline President Diederik Pen.

On Saturday, WestJet CEO Alexis von Hoensbroech blamed the union for the disruption, arguing that leaders refused to negotiate.

"Their only purpose was to disrupt as many Canadian travelers as possible," he said.

Pen told reporters on Saturday the carrier was expecting to fly around 70,000 passengers a day during the long July 1 weekend. He said the airline can maintain minimal service with 30-50 aircraft, operating around 150 flights a day.

The strike has frustrated travelers during Canada's long weekend with passengers taking to social media to complain about canceled family holidays or being stranded.

Canadian Labour Minister Seamus O'Regan has urged WestJet and the union to resolve their differences and reach an agreement.

Seeking to preemptively avert the strike, O'Regan had asked the Canada Industrial Relations Board to resolve the contract dispute through binding arbitration.

While the board agreed to arbitration, it said O'Regan's referral "does not have the effect of suspending the right to strike or lockout."

Oestreich said the union, which is in a legal position to strike, wants a negotiated deal instead of an agreement imposed by an arbitrator.

WestJet said it has offered a 12.5% wage increase in the first year of the agreement and a compounded wage increase of 23% over the term of the agreement. (Reporting by Allison Lampert in Montreal and Devika Nair in Bengaluru; Editing by Lisa Shumaker and Leslie Adler)