Hundreds of Canadian election observers will fan out across Ukraine on Sunday to monitor the integrity of the embattled country's early presidential election process.

Twenty-one candidates are running in the election, which comes approximately six months after the outbreak of protests that led to the ouster of President Viktor Yanukovych, and the annexation of Crimea in March.

Sunday's observation mission will be the third time in four years the Canadian government has sent a large delegation to observe an election in the troubled country. Here are three things to know about the mission:

Who are the observers?

The mission is being mounted by the Canadian Election Observation Missions (CANEOM), an Ottawa-based NGO. More than 1,500 Canadians applied to join the CANEOM mission. A total of 500 observers have been sent to Ukraine. Core team members include those who have had experience monitoring elections in Afghanistan, Bangladesh, Haiti and Mali. They will be joined by Senator Raynell Andreychuk, CANOEM’s head of mission, and former Ontario premier Mike Harris.

"This is an important election for the people of Ukraine, and an important election for geopolitical stability," Harris said in a statement on Friday. "We are here to send a signal of support to the people of Ukraine, so they know the world is watching."

What will they be doing there?

The CANOEM mission started with 39 long-term observers that arrived in late April. They helped lay the groundwork for the full-deployment of about 140 observers who will be closely watching the May 25 vote from "soup to nut."

"On election day, (the observers) are going to witness every aspect of it, from the formal unsealing of the ballot boxes to the demonstration that they are empty," Yaroslav Baran, the deputy head of CANEOM, told CTV News Channel on Saturday. "(Observers) will also witness the tabulation process….and the physical transportation of the ballots."

If a second-round of balloting is necessary, CANEOM will deploy about 240 observers to monitor a runoff. It will be held on June 15.

Where will they be deployed?

Observers will be present in all "oblasts" or provinces in Ukraine, except Crimea, the strategic region on the Black Sea which Russia took over in March.

According to CANEOM, the Central Election Commission of Ukraine has been unable to establish a polling apparatus in the region due to "ongoing Russian military occupation, intimidation and aggression."