The former England half-back is sure to be an integral presence once more as the West Yorkshire side face Hull KR and seek to retain the trophy they famously won 12 months ago.
McGuire was inspirational then as Leeds, having lost all six finals in which they appeared since previously winning the Challenge Cup in 1999, at last prospered by beating Castleford Tigers.
He said: “When I made my Leeds debut in 2001, if someone had said I would play at Wembley and make 400 career appearances, I would have laughed at them.
“Both are really special but to do them at the same time is a bit of a weird coincidence.
“I saw before last week’s game I was on 399 for my career and when I wasn’t selected, it occurred to me that the Challenge Cup final would be a great time to achieve such a milestone.
“The Cup final already is special but I’m just honoured to have played so many games for Leeds and my country as well. Hopefully, there’s a few more in me yet.
“These personal accolades are nice and you never get bored of them but the biggest thing is the team. I know everyone will say that, but it’s true.
“We go through a lot together; training every day, working hard and going through a lot of pain at times and it’s all for occasions like tomorrow.
“But I won’t look back on my 400th game with any pleasure unless we are celebrating with the Cup in the changing room afterwards.”
Leeds-born McGuire, 32, is Super League’s greatest try-scorer having crossed the whitewash 227 times and has won six Grand Finals plus three World Club Challenges with the Rhinos.
With a dozen caps for Great Britain and another seven with England, he is undoubtedly one of the greatest players of his generation.
Given a rare night off at Hull FC last week, he admitted: “I feel lucky to have represented the city I was born in and my country.
“I’m proud of every game I’ve played.
“The fact we’ve been in so many big finals and won so much is a huge bonus.
“I’m fortunate to be part of a great club and to have been in great teams, with great players who work hard for each other.
“It is not easy to get into games like this, a lot of hard work and dedication goes into it, so tomorrow will be another occasion I want to soak up and enjoy.
“We will be based in London come Friday and one advantage of having played in a few finals is we know the routine and we’re comfortable with what we’ll be doing.
“We know how to handle big situations and the key to that is staying relaxed. You don’t want to play the game too early, which is something we’ve maybe been guilty of in the past.
“By that I mean we’ve played our big game in the semi or peaked a bit too soon. This time we are staying relaxed and not putting too much pressure on ourselves.”
League leaders Leeds are hoping to secure the first part of an unprecedented treble for the club which would include finishing top, lifting the Challenge Cup and going on to win a first Grand Final since 2012.
Hull KR, of course, have not played a Challenge Cup final since 1986 when they lost to Castleford and have won it just once, six years earlier.
McGuire, who scored a match-clinching drop goal in last year’s showpiece despite a couple of broken ribs, added: “I’ll sleep, although I will be thinking about the game to come.
“Most of the boys are the same; there’ll be a few of us dreaming of scoring the winning try and lifting the Cup, but we’ll be trying not to get too carried away.
“You have to go through the processes and do your job for the team before you get the rewards.
“We have been good at doing that this year, but we have got a good team in front of us in Hull KR, who will be desperate to get their hands on the trophy and we are taking nothing for granted.
“The important thing is to play well on the day. If we do that, we will give ourselves a chance.”
When recollecting the first of his 400 games as a fresh-faced teenager, McGuire says he can remember it all very clearly.
“I came off the bench against Salford at Headingley in 2001 and it feels like yesterday,” added McGuire, who is approaching his fifth Challenge Cup final.
“If I’m honest, it has gone too quickly. I am trying to slow these weeks down and make the most of every game now.
“As rugby players we live week by week and look forward to the game at the weekend and this season seems to have flown by.
“It doesn’t seem too long since I was an 18-year-old running about in my first game. That’s almost half a lifetime ago, but I have enjoyed every moment.”
Chester’s legend note: Page 19.