The race for the Scottish Premier League title is all but over, with the Parkhead club holding a 21-point lead at the top of the table after Rangers were hit with a 10-point deduction for entering administration.
With Celtic having already secured a place in the League Cup final against Kilmarnock on March 18, the Hoops remain on course for a treble of trophies this season.
And Samaras is desperate to secure a second successive Scottish Cup title after clinching the trophy against Motherwell at Hampden last year.
"I put this game as number one in my list as the most important game of the season, because we need to defend our trophy first of all," the Greek striker said.
"We're proud to be Scottish Cup holders and we want and need to keep this trophy here at Celtic Park.
"Everybody is feeling good but we are looking at each game at a time and taking it step by step. So now it's this game.
"After Dundee United, number one in my list will be Kilmarnock and after that it will be Rangers.
"It's all on Tannadice just now. I think from Dundee United to the end of March, it's a nice schedule. We play them, then have the League Cup final and then Rangers, so there is great motivation for us.
"We are all in a team on a path and have set a target and we see opportunities and now we can make them come true."
Although Celtic's long winning run came to an end last weekend in their 1-1 draw with Aberdeen, Neil Lennon's side are still undefeated since the end of October.
The manager will be boosted by the fact he has almost a full squad to pick from, with only Mark Wilson, Daniel Majstorovic and Beram Kayal ruled out.
Opponents Dundee United are the form team in Scotland behind the Hoops, with their win against Inverness on Monday taking Peter Houston's side up to fourth in the SPL.
United are undefeated in seven matches and while admitting Celtic have an embarrassment of riches to choose from, Houston says his side will be going all out for the win.
"I'm not sure what Celtic team will actually face us," said Houston, whose side knocked out Rangers in the last round.
"They have a lot of strength in depth and will come out fired up on Sunday. Celtic are a quality team, even though they didn't play to their normal standard last Saturday up in Aberdeen.
"But we will also need to play a lot better than we did against Inverness if we want to knock Celtic out.
"We will make sure we prepare properly. One thing we can say for certain is that we will try our best to make a right good game of it.
"We'll be attacking to try and score goals. It's the only way to go into a game like this."
Also on Sunday, high-flying Motherwell take on Aberdeen, who are undefeated in 2012, at Fir Park.
On Saturday, there is an all SPL tie as Hearts host St Mirren at Tynecastle, while First Division minnows Ayr United take on their Edinburgh rivals Hibernian at Somerset Park.
Fixtures (1500GMT unless otherwise stated)
Saturday:
Hearts v St Mirren (1230GMT), Ayr United v Hibernian
Sunday:
Dundee United v Celtic (1315GMT), Motherwell v Aberdeen (1545GMT)
Source: AFP
Source: AFP