CBCNews.ca has full coverage of the Alberta and Ontario byelection results after polls close at 9:30 p.m. ET (7:30 p.m. MT)

Besides being the day that many Canadians will be taking off so they can have an extra-long weekend, today is also byelection day in four federal ridings.

Here are five things to think about before the results roll in at 9:30 pm ET (7:30 p.m. MT) tonight:

1. Scarborough-Agincourt and the 'Jimmy K' effect

Liberal Jim Karygiannis, who was never afraid to speak his mind while serving as MP for Scarborough-Agincourt, resigned to run for a city council seat in Toronto. (CP PHOTO/Fred Chartrand) Jim Karygiannis is the former Liberal MP the winner of this byelection will replace. He's probably not well known outside of his riding or the confines of the parliamentary precinct but, boy, did he have a way of blowing the dust off his knuckles. Never one to shy away from speaking his mind, Karygiannis definitely felt most comfortable fighting from the right corner of the Liberal Party of Canada.

So there was some concern for the party's prospects in Scarborough-Agincourt when Liberal Party Leader Justin Trudeau talked of legalizing and regulating pot and announced that all future Liberal MPs would have to be pro-choice. Karygiannis's hand-picked successor lost the nomination to Arnold Chan, which likely worried Grit headquarters.

Karygiannis eventually came around and endorsed Chan. Tory flyers that implied Trudeau's marijuana policies would end up corrupting the children of Canada probably helped.

Regardless, it's a three-way race. The NDP candidate is immigration lawyer Elizabeth Long and the Conservative candidate is Trevor Ellis, a teacher.

2. Trinity-Spadina: Do you want the orange sauce or the red sauce?

Among the many other things this cosmopolitan riding has to offer are restaurants — Chinese, Vietnamese, Italian, Portuguese, breakfast joints, haute cuisine, fast food and the faces and voices to go with it. But when it comes to federal politics, there are just two flavours: Liberal and NDP.

Full coverage tonight CBCNews.ca will have full coverage of the byelection results after polls close at 9:30 p.m. ET (7:30 p.m. MT). Follow our live blog after 8 p.m. ET (6 p.m. MT) in the lead up to results.

The riding was represented by former Toronto city councillor Olivia Chow, who resigned to run as a mayoral candidate.

The New Democrats are serving up Joe Cressy. He's young and the son of a former city councillor. His NDP credentials are impeccable. He was president of the party's riding association in Trinity-Spadina. He worked as Chow's campaign chair in the 2011 federal election and is a member of the NDP federal council.

And up until the Liberals presented their candidate, he was a shoo-in to win the riding.

Adam Vaughan left his Toronto city councillor job (do you see a theme here) to run for the Grits. Before politics, he was the city hall reporter for Toronto's Citytv and he did a stint at the CBC.

The two opposition parties have a lot riding on Trinity-Spadina. Since 1972, every time the Liberals have won the riding in a general election, they've gone on to form the government. Each time the NDP has won, the Conservatives have taken power. That probably explains why both leaders have spent a lot of time in the riding with their candidates.

3. Rural Alberta

Need we say more than that. Ridings in Canada don't get much more Stephen Harper Conservative than these ones. A loss for the Tories in either Fort McMurray–Athabasca or Macleod could signal a break in the space-time continuum or trigger a run on lottery tickets.

Fort McMurray's former MP, Brian Jean, stepped down to spend more time with his family. Given that he probably could have had the seat for as long as he wanted it, he's probably telling the truth about his reason for leaving politics.

Conservative MP Ted Menzies resigned his southern Alberta seat in the riding of Macleod to become president and chief executive officer of CropLife Canada, a trade association for plant-life technologies. (Adrian Wyld/Canadian Press) Down in Macleod, Ted Menzies left his minister of state for finance portfolio to take over the reins of CropLife Canada, an agricultural trade association.

The MPs in waiting are Conservatives John Barlow and David Yurdiga in Macleod and Fort McMurray-Athabasca respectively. Barlow is a newspaper editor who had to fend off criticism from the gun lobby during his nomination race. Yurdiga is a former Athabasca County councillor and reeve.

See ya soon, guys!

4. Voter turnout: How do I get to the polling station from the lake?

Byelections are rarely well-attended exercises in democracy. So they can usually use all the help they can get if lots of people are going to cast a ballot. Wedging voting day between a weekend and Canada's national holiday does not fall into the helpful category.

Advance polls were held in the ridings on June 20, 21 and 23. Numbers were down in all four ridings compared to the advance polls in the 2011 general election. Macleod had the steepest drop, going from 6,581 voters casting an advance ballot to 3,087. In Trinity-Spadina, there was almost no difference.

Earlier in the campaign, there were worries that the Ontario provincial election would confuse matters. NDP Leader Tom Mulcair called the timing "curious."

5. What constitutes a win?

Federal Liberal Leader Justin Trudeau, right, speaks to supporters with Trinity-Spadina candidate Adam Vaughan during a campaign stop in Toronto. (Nathan Denette/Canadian Press) Not losing.

"The NDP needs to hold Trinity-Spadina. If the Liberals win that, that's a big setback for Tom Mulcair," national affairs editor Chris Hall said on CBC Radio's The House on the weekend.

Hall said he will also be keeping an eye on how much opposition parties cut into the votes of the Conservative candidate in Fort McMurray-Athabasca. Oilsands development and the federal Temporary Foreign Worker Program are big issues in that booming riding.

CBCNews.ca will have full coverage of the byelection results after polls close at 9:30 p.m. ET (7:30 p.m. MT).